It's not hard to think how it would help, since free warzones = more people playing = more possible subscribers or people who use the shop. You would be surprised of how much the average american joe spends each month on f2p games.
This games does not survive through subscription, don't lie to yourself.
I know it doesn't survive by subs anymore. They actually want everyone subbed and doing micro transactions. They will do everything then can to fleece people, but that is good business sense. The bulk item packs show how far they will go, it's deplorable but profitable to suck in gamblers.
Free warzones, would give lots of subbed pvpers the chance to unsub and still do what they enjoy.
Then next up would be pve, as was said a few posts ago.