Is it advisable to tell your partner everything about you.Why should we? or Why shouldn’t we?

Hmmmmm, personally i feel we should, but after talking with  some people , i was able to deduce they are of a different opinion.

Some people believe its not everything you need to share with your partner or spouse  because they worry about them turning around and using it against them?

Some believe also that what happened in the past should stay in the past but what if the past comes up in the present and could destroy your future

Please whats your opinion