Ommidiam

i feel like this is a bit misleading. yes, you can game and fold at the same time, tough only if you have multiple GPU's running in your system.
if you have a standard gaming machine with maybe one GPU, you can't fold and game at the same time.

That's actually pretty cool. I typically just disable the GPU when the computer is in use, and disable CPU processing when CPU usage is over 30-40% (which means all games will stop both GPU and CPU processing.)
 
I wish there were a program to let you better control CPU %s for BOINC projects. Like I REALLY want to be able to schedule my computer to only use 50% of the CPU during the day, but use 100% at night. 

Really depends on what you play and to what degree you are willing to accept game play at.
I've actually played and F@H on my 1070 at the same time however when it came to a specific event like for ETS2/ATS Xmas event I stopped it because it made life easier to complete the event. Just launched ATS and there was stuttering and FPS loss but I didn't change the current settings I had for during the event either:

 
That said I had a avg of 50 fps and even w/o the game loaded my system is at 100% CPU and 70+% ram, also didn't notice a real drop in folding performance either during that time. Once Witcher downloads in 2 ish days time (bad internet, not a bad time to buy the game tho on steam ) I'll try to play it with F@H running as well.
 
Oh and cars can fly...

 
So it really becomes a balance of what you are willing to accept along with what your computer can handle.