Here is my summary during the -7A build.
1.5" yolk, sometimes while riveting always while dimpling
3" yolk, I use this most of the time for riveting
4" yolk, I use occasionally but still a yolk I like to have
4" no hole, this comes in handy on trailing edges but the only reason I have it is because I bought a pure piece of c-r-a-p squeezer from ATS, dang I hate that squeezer. It's the only yolk that goes on it though. I digress...
longeron yolk, an absolute must have. You can do a lot with it but there are definitely times you don't have the space for the yolk.
Can you get by with less than the yolks I have? Without question! However, I like to squeeze when I can before having to buck, it's not that I can't shoot them but it is just easier to squeeze in my mind.