What Does Russia Get From This?

Kiev had already granted Russia the right to use bases in the Crimea, which is the only warm-water port Russia has available.

Now what?

If Russia annexes the Crimea, they get the status of international pariah and gain bases they already had.

If Ukraine manages to kick the Russian troops out of the Crimea then they are also likely to end the Russian basing privileges too.   After all, they can say, "Last time we let you keep troops here, look what mischief they got into"?