The following information is regarding TuneCore's Publishing Administration service
Yes. By registering now it assures that when you do release your music; your royalties as a songwriter it makes it back to you. Nobody can claim they did not know it was yours and give it to 3rd parties
Keep in mind, although your compositions will be registered, no royalties will be received since you have not yet released your music. Once you release your music and begin to receive sales, streams, etc. the publishing royalties will begin to flow through.