This depends on your target platforms. Is this a standalone game, or will it run in the browser, or on mobile phones?

In any case, it's a good idea to reuse assets in multiple levels when you can, but at the same time try to keep the amount of different assets used in a single level a bit down if size is any kind of limitation.

This is of course very general advice, but it's hard to be more specific without a more specific question.