In contrast to a traditional publishing company, a pub admin manages your musical works for you without you giving over control.
They’re typically more flexible than traditional deals and allow you to retain ownership of your songs.
So do you need one?
Unless you have a publishing deal and/or completely confident that you are collecting all your royalties, than a publishing administrator can give you the peace of mind that your compositions are being properly handled.
As always, read the fine print and do due dilligence.