Just in case you missed this excellent post about how to use Recount to its full potential (we also snuck it in our Daily Quest column a little while back), it's definitely worth a look. Most players just use Recount to check their own damage numbers, but as 4 Haelz points out, there's definitely a lot more to it than just that. Not only can it be used to examine overall output on fights and instances, but you can use it as a tool to monitor what kinds of spells are producing the most for you, and how your damage or healing output changes over time. You can also have it track who you've healed the most, or which targets you've really gone to town on, and you can then make adjustments to your play style from there.
Now, Honor's Code has another great post about the addon, this one specifically for tanks. Recount will actually let you bring up a "Death Report" feature that will allow you, as a tank, to suss out exactly what went wrong on that last wipe, whether it was something you were late on, or whether your teammates should have done something that they didn't. You can even broadcast that Death Report, so you can show the person at fault (of course you have to be tactful with this -- you have to make sure the person you're "correcting" understands that you're just trying to get better, not attacking them) exactly what happened and when.
Recount is such an excellent addon, and so many of us just use the top level functions of watching the meters (sometimes to the point where it isn't helpful at all). But used in the right way, Recount provides a treasure trove of information on what you've done during a boss fight, and how you can make yourself and the rest of your raid even better.