I think I have seen Microsoft account and Windows account.  Are they the same thing?

My question is whether having multiple Microsoft/Windows accounts to be avoided, because I think I do?  I see a common recommendation to use your Microsoft,Windows account when entering a new site, but never an explanation why.

If I should reduce the number of accounts, how can I find where they are and what I should do with them?  It seems to me a matched Email address and password could have some value.