I almost always have a beer or maybe two over the course of the brew session. Or, often, I will pour a flight of 4-6 tasters (3-4 ounces) of each beer I have on tap and sip/sample those over the course of the session.
I will say this - almost EVERY stupid mistake I have ever made while brewing was when I was getting on into the 3-6 beer range. My biggest screwups have been when I have brewed with a good college buddy - we have shot for 3-Batch days a couple times, drinking too much....... we have yet to get all 3 into the fermenters due to some stupid mistake (knocking over a bucket full of wort, leaving the flame on and cooking the mash, stuff like that).
0-1-2 over the course of a brew session is going to give you the best chance of making good beer. Beyond that, eventually you are going to screw something up. Might be minor, might ruin your beer, might put you in the hospital....... might burn your house down.