[Ghazban]

It depends on a given player's situation. If you have one style that works well for you in the game you're playing and have no plans to ever change games, you have no reason to play a different style.

If someone wants to be the best overall poker player they can be (independent of financial results), that person should obviously learn every style (as well as every game).

For a player with aspirations of moving up to the biggest games around, being able to play all styles in all mindsets is necessary to beat those games (by that, I mean being able to play well in all styles despite whatever else might be going on in the game; many players will revert to their most comfortable style when something unfamiliar happens at the table).