My question is about what Russia has to gain from taking Crimea.

Crimea is a very strategic province both militarily and economically, but why would Russia occupy it? They are in no danger and are, in fact, farthest away from any conflict, so this is not a "protection of Russian people". It might benefit from their economy if they loot the area, but that would destroy the existing Russian support in southern and eastern Ukraine. The only thing that makes sense is that this is:

A) forceful seizing of a Ukrainian province, or
B) display of power/insult to western world.

If Putin thinks that Ukraine is about to transition to pro-west even with Crimean pro-Russia voters, he may take those pro-Russian provinces rather than let them be controlled by Kiev. However, this could be an attempt to show how benevolent the motherland is toward Russian supporters and destroy the western support (although I don't think that will work). If this is simply a display of power, he might go ahead and loot the area and screw with some Crimeans if he feels like it.

But I don't know the actual answer.