100% dependant on the situition. I know that doesn't help but you really just have to calculate to determine if you can afford the lost of time, or if you can ignore the counterplay you might be giving to your opponent.
Prophylactic move vs loss of one 'tempo' and the attacking initiative
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I don't consider myself as a player who plays prophylactic moves so my personal opinion as a huge attack lover is that ATTACK!
There are some "automatic" prophylactic moves that I do: I remember to play a6 in the sicilian defence if I'm playing with black or to play h2 in the Ruy Lopez or the italian game, when playing with white. Those are normal standard moves and they are "in the book". But my doubts specially begins during the middle game and in fast time control games...
I think this is a good question -- although it is a question that even GM's would ask themselves in certain situations. As jdcannon stated, it's certainly situational, and in the end, a player's "style" may have everything to do with the final decision.
Think Karpov vs. Kasparov.
This is one of the trickiest things about chess.
I would think that if the initiative leads to a forced line you have calculated, which is winning, you keep the initiative. The less sure you are of your planned attack, the more likely you would take a prophylactic/waiting move.
In many games I face this dilema: should I do a prophylactic move but that could cost me the attacking initiative (something that I enjoy to have during the games) or not? Generally speaking, what do my fellow chess.com players think about this, if you are playing to win?
Cheers :)