Holding that many assets active in place is very expensive. Putin probably has a timetable.
It costs Putin nothing to drive ten or twenty artillery pieces back and forth along the border. They have no targets to shoot at, and they have no offensive value that I can comprehend. However they have plenty of value to scare the new government in Kiev - the government that has no experience in governing and that has no support from the Ukrainian Army (and that has no Ukrainian Navy at this point.) This activity is just to fill time before Crimea can vote on a referendum that is scheduled for March 16, in about 3 days from now. Its results are easy to predict, if opinion polls in Crimea make any sense. Crimea may be given considerable trade preferences.
Once that happens, the new government in Kiev will have to explain to the remaining (so far) Ukraine how they managed to lose Crimea. It's not a good plan for a politician to begin the reign with a major loss. Ukraine may easily lose several other Eastern provinces; if that happens, Crimea and Russia will be connected with a land corridor. It is not unreasonable to think that this may happen - Ukraine is so poor (due to mismanagement, not due to lack of resources or of educated workers) that merely joining Russia already boosts the income of the population. After the dust settles, Westerners will only have their historical territories, and they will be surrounded by people who have centuries of animosity against them due to the complicated nature of many land grabs in the last 1,000 years.