It depends on the prompts and the limits. For some of the classic prompts, like diversity or a challenge you have overcome, the limits would vary a bit between schools, say 200 words vs 300 words. For those, I would re-edit the essay to be close to the word limit.
Other schools give you some really large limits (CU with 2000 words, VCU last year with 8000 characters) - I would not try to match the content to these. Chances are that they are that large as a way to allow flexibility when needed and that most candidates won't come close to them. Adding fluff to your essay in such situations will make it worse, not better.