Just to chip in to that "Full Power right away" list of comments...
Sometimes that trope is done right, most of the time it isn't. One reason not to fight at full power from the start is to gauge your opponent, and figure out when you could best use that one attack that would decimate them, or to avoid overexerting yourself by getting your powerful attacks dodged early. Alternatively, there's the infamous "battle of attrition" where you convert your full power into a goal to just tire out your opponent before you tire out yourself.
Unfortunately, that trope is misused far too often, and the reasons for not fighting at full power are rarely given, and even more rarely make sense. "Ha! You're strong, let me fight at full power then!" That is the single most overused reason given for that trope, and it's the one that makes the least amount of sense.
Then again, we are talking about a media where it is normal to call your attacks before performing them.