Yeah they can catch you off guard if you are not ready. It's too bad that often I get called in quite a bit after projects are done when things like this are desired but are not done during the project. I have to be the guy to tell them it would have cost thousands less if given thought during the build (only when they ask though).

Transfer switching isn't the issue, check the price difference between setting up automatic transfer switching and manual transfer switching... It's a good way to add some dollars on the project. I have replaced so many of these style switches that I have lost count

[Link: homedepot.com]

But some people want to hunt for the flashlight to flip the switches.