When I was a kid we had a family stereo system on which the speakers could be unplugged from the unit.  Somebody (I think it was my Dad, but I'm not sure) told me to never turn on the stereo when the speakers were unplugged or you will burn out the electronics in the stereo.  Keep in mind this was 1964 and vacuum tube electronics.
 
Fast Forward to now.  I have my Focusrite interface and I always feel as if I have to turn on my monitor speakers whether I use them in a session or not because I'm afraid that I will fry the circuitry in the interface.  Something inside is telling me that it's probably no big deal now. It may have been an issue in 1964 vacuum tube technology, but not now, but I need some affirmation on this from somebody in the know.
 
I can't see having my speakers on if it's not necessary (like during a vocal tracking session or the like).
 
Thanks!
John B

Most (all that I've seen) tube amps need a load (speakers) attached or there can be damage. 
Most solid state amps are direct coupled and an open (no load) is not an issue.  What you have to watch in a solid state amp is that the load impedance does not go too low or there is potential for damage.  Too low impedance can result in too high current flow and cause circuit damage.    
 
With a recording interface connection to studio monitors its a non issue and the speakers can be powered on or off and no damage.  Studio monitors are self powered speakers and just receive an external low level (approx. line level) signal and amplify it internally.  

fireberd
 
 
With a recording interface connection to studio monitors its a non issue and the speakers can be powered on or off and no damage.  Studio monitors are self powered speakers and just receive an external low level (approx. line level) signal and amplify it internally.  

Yeah, and considering that I do have the headphones plugged into it it's not like there's nothing going out of the unit.
Thank you so much, fireberd, for your explanation.
 
JB

Well the Analogue outs of my Focusrite Pro 40 and 26 I/O were never used.  I always feed the output of either SPDIF or ADAT's to my Mixer which connected to my Monitors John.  Not had a problem yet (he says touching the wood in his furry bonce) 

Tube power-amps need to see a load from a speaker/load-box.
You can have a tube in the preamp section of an otherwise solid-state amp... and it'll be fine without a cab plugged-in.
 
Paging @Tom Deering!
This is your area of expertise.  

Interfaces are fine with nothing plugged into the outputs, at least I’ve never heard of one that has a problem. They’re basically preamps as far as the amplification side of things is concerned and designed not to require an output load to avoid damage.

The rule of thumb with power amplifiers is that valve circuits won’t tolerate an open load for very long at all - maybe no longer than a few seconds depending on how good the output transformer and other components are. Without a speaker/load connected the output transformer starts complaining loud enough to hear and the power amp valves can start spitting and shorting internally. Like most guitarists I’ve accidentally switched on an amp head when it’s not connected and you really can hear it complaining.

Solid state amps on the other hand will be damaged almost instantly if the speaker connection is shorted out, but can tolerate no speaker being connected - they just see it as an infinitely high load and are happy. The exception being solid state amps which have a output transformer like a valve amp does, but these are very few and far between.

tlw
Interfaces are fine with nothing plugged into the outputs, at least I’ve never heard of one that has a problem. They’re basically preamps as far as the amplification side of things is concerned and designed not to require an output load to avoid damage.

The rule of thumb with power amplifiers is that valve circuits won’t tolerate an open load for very long at all - maybe no longer than a few seconds depending on how good the output transformer and other components are. Without a speaker/load connected the output transformer starts complaining loud enough to hear and the power amp valves can start spitting and shorting internally. Like most guitarists I’ve accidentally switched on an amp head when it’s not connected and you really can hear it complaining.

Solid state amps on the other hand will be damaged almost instantly if the speaker connection is shorted out, but can tolerate no speaker being connected - they just see it as an infinitely high load and are happy. The exception being solid state amps which have a output transformer like a valve amp does, but these are very few and far between.

Makes me glad I'm not a guitarist.

Unplugging the speakers on your 1964 system meant disconnecting the speakers from the amplifier. Your current active studio monitor speakers contain their own built-in amplifiers and these are permanently connected. Disconnecting the studio monitors means disconnecting the amp from the source rather than disconnecting the speakers from the amp. It's a totally different scenario.

Kev999
Unplugging the speakers on your 1964 system meant disconnecting the speakers from the amplifier. Your current active studio monitor speakers contain their own built-in amplifiers and these are permanently connected. Disconnecting the studio monitors means disconnecting the amp from the source rather than disconnecting the speakers from the amp. It's a totally different scenario.

Please note that I'm not concerned about the health of the monitors, only the interface.
JB

John, your question has been answered;
No interface, to my knowledge, includes a power amp, so no problem.
As to tube amps, that’s been covered; you MUST have some kind of load.
I don’t work on solid state gear, so I won’t comment; only that I would probably connect a load if I was going to “scope” the output.
I would “assume” that there is some kind of interaction in any power stage and it’s load.
My nickle98’s worth.
Enroute home from the fall tour, a weeks worth of work, then I can retire to my studio and give my new “Cat” some exercise.
I can hardly wait.
I’m pretty sure the M.2 is “anticipating” my every move and getting ready to load Superior, Trillian etc. as I write...
T