Yes! Even if you are the songwriter and the only performer of your songs, release details will help. These additional details – like ISRC information– better help collection societies match your songs to the royalties they have generated.
If you distribute your music through an online service like CD Baby – rather than being released on a third-party record label – you will still be assigned an ISRC and some other helpful details. If you're having trouble locating them, contact your distributor directly, and they would be happy to provide them to you.
Be sure to add these to all songs you register!