Not only worth it, it can be very profitable to start out this way. The micro players are usually people who have won money in a freeroll or something like that. Mostly casual players who don't really study the game itself. They may know the theory, but understanding and applying it to real life situations is difficult because they lack the experience/disassociation to see things for how they are. Not only that, but as someone said above, it's by far the best way to gain general experience for cheap. Just don't expect the style of play to match the style in the bigger buy ins.