An optimal strategy’s goal is to loose the least against any arbitrary strategy. It is a strategy that is impossible to exploit in poker because poker has antes.
Poker players must seek maximal strategy. A maximal strategy’s goal is to win as much as possible against a specific strategy.
For example, you would raise more often when the antes are higher, regardless of the other player's strategy.
The optimal strategy beats everything but an equally good strategy, and ties against itself, but it doesnt necessarily maximise profits against other bad strategies.
If you are able to identify flaws in your opponents strategy then you can play non-game theory optimal to increase your profits against that perceived strategy. Doing so comes at the cost of you yourself no longer playing the best strategy though.
There exists strategies that gives higher yields vs certain unbalanced strategies than the game theory optimal strategy (or strategies - for all we know there are several optimal strategies in limit hold'em).
For instance - in limit poker if your opponent will never raise, call every street, but not call the river with anything less than a pair, regardless of what you do, then bluffing every river is a more winning strategy than the game theory optimal strategy. The game theory optimal strategy would include times when you do not bet the river, for balance, but knowledge of your opponent's flawed strategy would tell you that betting 100% of the time has a higher yield.
I'd like to add that how poker players generally define as their main goal, to maximize expected value: http://en.wikipedia.org/wiki/Expected_value