Once you've installed WordPress, the WordPress database user does not need the rights to do any database structural changes but only need to read and write from and on the database. If you have a plugin which needs to create a table in the database, then you might need to have alter rights as well, though only the first time when you install it. You can safely remove drop and alter access to the user. You can strip much more privileges if you want but to start on the safe side, you can remove those.
After making such changes, please double check your blog functionality to make sure it is still working fine.