There's something to the health strategy a lot of people overlook though. At lower skill levels, it gives you a bigger margin of error for positioning. At the highest skill levels, such as pro teams/challenger tier, it dissuades the other team from focusing on your damage dealer too much, so over a longer engagement you end up doing more damage since you live longer. With pros, they dance back and forth between fighting/running away over and over.
In between those skill levels, it's not quite as effective. If someone gets caught just a little bit out of position, and your team doesn't have the upfront burst/coordination to punish them for it, they end up getting away. Pros don't need as much dmg, because all 5 of them will react almost immediately to the same thing, whereas amateurs in higher ELO (Gold+) might have only 1 or 2 of the team reacting at the same time to the same thing.
This is why glass cannon fed builds will carry games so hard. Due to the other team's lack of coordination, you end up having these mini 1v1 fights instead of a concentrated 4v1 on you. If you put out enough damage, you own one guy in 2-3 seconds before the other team member reacts to assist him, then repeat.
That said, I do tend to get warmogs early on quite a few champions due to it's efficiency. Especially on Katarina when I play top. Her AP scaling isn't that great, but her base dmg is and she really needs resets to do insane damage in a team fight anyways. If you go too glass cannon, she dies too easily and you don't get resets. One reset letting you do a whole other Q>E>W combo is worth more then a 2k AP item would do to your initial combo. If she lives long enough to Q>E>W out a couple times, along with your team's damage.. she should get a reset and snowball the rest of that team fight. Basically, the longer she lives, the more damage she does anyway. I should clarify that I always get either haunting guise or sorc boots before the warmogs is complete. All depends on the lane, sometimes I gotta go hextech first for sustain, but generally those 3 items are first ones built, in some order also depending on how game is going. If our jungler is a strong ganker and helping my lane, I'll rush the sorc boots and/or haunting guise first.