Bulking up (getting fat) = eventual decreased insulin sensitivity at some point, still waiting for someone to explain to me how you can grow faster (muscle) in this state.
You also have to consider how the person stores bodyfat too, some people store it pretty evenly so they can get a little chunkier, some people like me store it in one area in globs. These people have to be really careful because it is already hard to get that area down, now you go add 5% fat to it…prepare for 12 weeks of hell. Getting that tough area down will likely hurt other areas.
It’s also knowing your body. Eventually you get to a point where you keep raising calories and you aren’t even sure if you are even gaining muscle, you can just see fat accumulation. Gaining 5 lbs of fat to gain 1 lb of muscle is a bad idea. You will lose that 1 lb of muscle trying to get the 5 of fat off.
Getting fat over and over can make getting leaner harder each time. If you overdue it, then have to kill yourself to come down, what do you think your body’s first response is going to be when you start your next diet? Yes, survive and hang onto that fat.
I personally don’t see any reason to get above 12-13% for most guys. Personally I stay under 10%. Ultimately it will depend on where you start to lose insulin sensitivity, pumps decrease, muscle start getting softer, etc. There are signs if you know what you are looking for..