There are tons of different music "publishers" out there. All bring different pros and cons.

Lone-Wolf: Acclaimed Songwriter or Producer who will pitch getting you placements but will likely make your business convoluted.

(Cont.)

Admin: Won't offer much creative services but won't own anything. Pitch will be collecting all of your royalties globally for a small fee.

Investment/Banker: Has the capital and sees the profit in royalties but won't offer much other than capital. Wants ownership.

(Cont.)

Full Service: Normally pitched via co-publishing deals. Your Warners, Sonys and Universals. Will offer capital and creative opportunities but will own a piece and control your catalogue for a while.

All could make sense at different points in your career.