It would be easier to arrest for possession if searches, seizures, and arrests didn't require probable cause, and police could just arrest anyone, anywhere for any reason or none at all -- and search anything anywhere without consent for any reason or none at all, and use any evidence so obtained in prosecution.
Much of the Bill of Rights -- and much of the concept of individual rights against government underlying and preceding it -- is based on the belief that making it easier for the government to arrest and prosecute people even for things that everyone agrees are bad is often less of a benefit than the powers granted to government in order to achieve that are a harm.
So that's at least one school of thought on how this could be good even though it makes it harder to arrest for possession, even if one things that arrests for possession (where actual possession occurs) are a good thing.