One takes the time one must in order to survive, with chances at least, till the next move. What profit it a player to be lost by move 18 and still have 67 minutes on the clock?
"Clock management" is not about spreading one's time out so much as not wasting it by dithering (as opposed to investigating promising/interesting lines) or trying to force a good outcome to a line that catches one's eye but seems to have no good outcome.
If, however, one saves a minute on move 15 and makes the second, third, etc. best move, there's no tomorrow as the best players usually see and do the line that breaks one. But do not later get careless and blunder queens giving one a miracle chance to get back into the game.
I hate hearing people whine about losing on time. As if they'd've won if only they had twice the time their opponent did. If instead they'd've moved sooner so as to not lose on time with the same time their opponents had, they'd've lost "on the board." Either way, they lost because they weren't as good as their opponent was that day. Hanging on by your fingernails only to fall in the end anyway might make for a better adventure story, but the other guy hung on and you didn't so... you're not the better chess player just somehow done dirty by fate.
An interesting related fact is that by consuming all your time, you often force the opponent to not use his time fully as, of course, you're allowed to think while he thinks. Even at, say, move 35 with you having 28 seconds, he still can't simply do something very complicating so that your hurried moves include a blunder as he must do the same and risk doing the same. So by consuming your own time fully while he holds back you achieve the taking of time from him perhaps to your advantage. Naturally, he CAN stop and take the half hour to think giving up his "advantage" on time, if he must to avoid catastrophe, but players don't seem to do so.
Since the literal hallmark of "the best" players is that their moves build situations in which, say, ten things are going on as each player tries to finally overtax his opponent's ability to respond... literally building to be the one who moves the "straw that broke the camel's back"... it is not surprising they must spend excess time earlier when there would seem to be more chances for such. But it's not the complexity itself that requires it. It is the fact that stinting on thinking then means no game later. One must reach his 22nd birthday to reach is 73rd birthday.