Do you need to cancel a previous will when rewriting it?

Answer 1

Generally, you should cancel the prior will if only to ensure that there is only one last will and testament to avoid confusion. The rewritten will should have a clause in it that specifically revokes any and all wills made before this one.

If the rewritten will does not revoke all prior wills or if prior wills are not revoked by some other means, the prior will may be only partially revoked to the extent that the rewritten will is inconsistent with the prior will. That could have some unintended and unpleasant consequences.