Noel Borthwick [Cakewalk]
There are several advantages and reasons why you should leave auto rescanning on:
 

• You install a new SONAR update that includes new PC modules. (New Prochannel modules or region fx won't be seen unless scanned)
• An update made a change to a plugin that changes its behavior (e.g. it could add sidechaining)
• You have VST3 plugin sets/shells like waves where multiple plugins are bundled into one dll. If you authorize a new bundle, on next run SONAR will automatically activate the plugins you bought.
• You can install plugins while SONAR is running and it will pick up the new plugins automatically
• If you change your VST scan path to add a new path, it will automatically add any new plugins dynamically
• the process is *very* lightweight and doesn't slow down the start of SONAR. Rescanning is done on a separate process and the checking for updates is also very efficient.
• It only scans plugins that have changed since the last check so its very fast

 
 

I only had 5 items as reason to use it. 

Iv'e had it set to scan in background ever since we've had this option. With a raft of plugins there always seems to be an update of something connected to Sonar and now there's a monthly update to Sonar as well a new plugin each time.

Thanks for all the information. It's definitely clearer now ... and I'm less paranoid ;-)

Clearly from the responses, ABS is a feature that illustrates how differently we all use a product.  My tendency is to be linear, conservative, and slightly paranoid about any process running while a client project is on the clock.  In other words if I added plug ins, I'd be doing that off my production time, and would not have Sonar open at the time.  Since I use multiple DAW's I also like to test the plugins in other hosts before considering them 'in - production'. 
 
Yesterday, after the I did the current updates Sonar hung at startup (during the plug in scan) .... oh well, there's just another log on my paranoid fire.  :) 
 
BTW loaded perfectly after I restarted Sonar ..... of course!
 
-D

The VST scanner should not hang SONAR itself. Even if a plugin hangs it will hang the scanner which is a separate process but not SONAR. What did you see in SONAR while it was hung? Was there a scanning toast notification being displayed?
Also make sure that you have the latest VST scanner in the shared utilities folder under Program Files\Cakewalk. The version number should be 5.0.7.1 and date should be 3/23. 
Its perfectly ok to not install plugins during a session of course but there should really be no reason to disable the auto scan since it will be idle in that case. Scanning never runs until something updates a file in the vstscan path. Overall by disabling it you are just making more things for you to remember to do on each update :)

I always leave it to auto-scan, and as Noel says, it doesn't do anything unless there is a change, and even there it only scans the plugins that have changed.  That takes almost no time at all, and seems to happen separately from Sonar becoming available to use while that is happening.
 
Bob Bone
 

Surely just detecting a change takes CPU cycles which means it is doing something?

Doktor Avalanche
Surely just detecting a change takes CPU cycles which means it is doing something?

Yes it is doing something. However, if you have ever sat and waited for a VST scan to complete before you are able to do anything with a program you will see how useful and slick CW's approach is. At present I don't worry about the VST scan at all in Sonar. I dread having to start programs that have a non configurable scan. Vegas Pro has a simple scan that can not be turned off.  

Right so CPU cycles vs convenience then? For me it's not hard to trigger a scan off after a software install.
You don't have to wait for a manual scan to complete BTW, it too will run in the background.

Doktor Avalanche
Right so CPU cycles vs convenience then? For me it's not hard to trigger a scan off after a software install.
You don't have to wait for a manual scan to complete BTW, it too will run in the background.

Not with other software. And the amount and time the CPU is used for the scan is trivial in Sonar. In other programs one can't do anything until the scan is complete. 
 
There is simply no reason to argue about this its a proven improvement that will save time.