I have a mental block when it comes to expanders, I don't know why. Therefore my eyes glazed over reading this, even though it looks like it might be of interest. Can anyone tell me whether it's useful or nonsense? 
 
http://noisefloorav.com/w.-i-use-expanders-on-dis/

Hi James, 
 
Firstly I'm not sure what would sound better, the raw big portion of noise, or the compressed smaller portion.
Sure you hear less noise, but it might be the rest of the mix suffers from the compressed portion of noise / fighting to cut through it.....this is something I'm not sure of but just thought it could happen.
 
Then you would need to add an expander which could give you latency.
And then maybe that noise would actually be nice in the mix, the last thing that would be a problem in my personal mixing (if that ever took off) would probably be noise.
Probably DAWS would have such a function if anything like this noise reduction would be good, I'd say.
But it's always good to read and think about things, thanks for sharing too.

 I think his goal in reducing the noise was to stop the amount going into the amp sim. 

Best place to put an expander/gate is immediately after the guitar. Much of the noise that comes from amps or amp sims is the original guitar hum/buzz that's now amplified and the potentially negative consequences of using a gate/expander are much less if the noise floor is as low as possible rather than trying to gate out a much higher noise floor post effects.

Keeping the amp gain low can help a great deal with noise, even if effects between guitar and amp are a bit noisy. Which is one reason why many guitarists prefer a clean or "edge of breakup" amp then use pedals to get fuzz/distortion/compression.

The Boss NS2 noise suppressor pedal is an expander which takes things further by having a loop that you put noise-generating pedals in and the loop is only open when there's enough signal at the pedal input from the guitar to open the gate. Set up properly it can block noise quite effectively, though dynamics and sustain might suffer a bit, especially if the noise floor is high enough to compete with the guitar signal as sustained notes fade out. Then the choice becomes live with the noise vs. reduce the available sustain but also reduce the noise vs. rethink gain staging and try and find a less noisy order to put pedals/fx in.

If using an amp sim, I'd track without a gate/expander then insert one as the first processor in the track if it's needed afterwards. That way any potential latency increase is irrelevant.

Noise is not good unless it's an artistic decision to have it. It can really make a mess of a mix because it restricts what you can do if you don't want a mix that's full of noise. There's a reason why good amp, effects and mixer/preamp designers put a lot of effort into designing circuits that have as little self-induced noise as possible.

Pete Cornish's website offers some useful thoughts on why a high noise floor is unacceptable, especially if it's going to be amplified by a big PA.

I use the PC4KExpander/Gate on problematic guitar tracks, first in the chain.

I find setting it to expander much more effective than gate. It reduces noise but reduces the risk of artifacts such as chattering.

Expanders can be excellent in many ways. Like a slightly higher noise background with a vocal track. But noise from a guitar being cleaned up is a great way to ensure all the quiet parts or no guitar playing at all then the noise level of the rest of the processing is still be low. I have got rack mounted expander that is easier to set.
 
And yes even a slightly noisy signal will still pop the noise through once the expander is at unity gain but the signal will most often mask any noise at that point.
 
Chattering can actually be reduced to almost nothing by adjusting any gate hold times if they are available and release times too. Having an expander close its release portion smoothly can be important. Chattering happens because the expander shuts off fast and then bounces back letting any tiny amplitude increases open the expander again etc..

I was using spectral tools to clean up my DIs, but it might be better to use that as well as an expander. I'll have to test it, but it might be better to have 2 things doing just a little work than 1 doing everything.

Chandler
I was using spectral tools to clean up my DIs, but it might be better to use that as well as an expander. I'll have to test it, but it might be better to have 2 things doing just a little work than 1 doing everything.

 
This is a good approach and in a way this is what I was doing. I had to record some super quiet voicers in my Melbourne studio (relaxation) and the noise outside was just a little loud for such things. At first I started removing the unwanted noise using a noise reduction approach, that worked OK but took time etc.. Then I just ended up setting a downward expander (hardware) really well just before the A to D in my setup. I found I was able to get virtually noiseless results this way. Sure the noise was still there with the spoken word but it got masked rather nicely in the end.  You tend to notice noise when the playing has stopped or the voice has gone silent much more.
 
Setting up an expander after the guitar and before any processing I would imagine could have a similar result. Nip it in the bud so to speak. And hopefully any buzz etc that is there will be masked by the main sound when it is present.

So what about just manually editing out the noise between phrases? Is that more common? I may try out that Boss NS2 because I do have a problem with a noisy Telecaster. 
 
I have to say though, sometimes I quite like that noise in between phrases. I'm working on a track now that has a section of just drums with some intermittent guitar phrases, and the buzzing in between phrases kind of adds to the whole atmosphere and creates more of a "live" sound. 

Of course it is all a creative decision. Once you start really cleaning things up then the sound gets to be more studio like I guess.  But in some situations downward expanders can be a godsend too.  You can use them on toms say but then you start losing the spill effect which you may actually be after.