Reloading to the max enables you to win the max possible amount from other players. If you think you have an edge over others at the table, you should be happy to have the largest possible amount of chips in front of you. When you first sit at a table or whenever you sink below that max buy-in threshold, you should want to top off your stack.
On the other hand, if you're less comfortable with post-flop play, you might want to play slightly short, so you have easier decisions (often shove vs fold decisions).
As for your comment about tracking your bankroll... you should be using PokerTracker or similar manager software. It will track all your hands in real-time on most online sites, so there's no problem with topping off as often as needed.