I wouldn't do abs before workouts and I never do them more than 2 times a week. If anything i save them to the end of the workout, as they are part of your "core" (god did I just say that), but they are paramount in support, power, stabilization for way more important moves like squats, deads, rows, hell basically all of your other compound work really. I find that one arm rows put a ton of stress on my abs in order to stay in a power supported position with some lordosis. Not to mention front squats. I have a little bit of ocd here and there, and nowadays I don't really like to work my abs even the day before squats or deads. Maybe that's over kill but that's just me. And frankly as many of us would tell you, ab work is just so optional if you're doing good proper compound work that it's not even worth talking about for alot of us. I do do direct work but I haven't done any in about a week.