Before the 5000 limit was begun, I had racked up 13,800 souls on my watchlist.
Suddenly I was in non-conforming status. I kept getting warnings about the dire consequenses of my HUGE watchlist.
Since then, I have slowly whittled down my list, eliminating all but direct ancestors. I've cleaned it up from the first abut 1500, up to 1822, I'm down to just over 7800 and I've never noticed any slow down in my browsing.
I try to orphan a few daily, after re-sourcing them, and adding anything I can find. I'm trying to leave them better off than they were, so to speak. I know in many instances I've found spouses, and children that I didn't have originally.
Its a recommendation, not a requirement.