Gives you the ability to start PVE in PVP gear and replace/upgrade pieces as you climb. You can upgrade your gear to 606 ilvl from M0, normal raid, etc. crests (which is high enough to begin heroic raiding, etc.) PVP gear is champion gear, so I believe you can cap it at 619 ilvl, but if you’re 590+ ilvl you should be able to do Tier 8 delves which (you can do them with a buddy to make them easier if you’re a bad solo class) gives 616 Hero gear in vault each week.
You also get base 603 champion (sometimes 610 hero) gear by using a key on the epic chest at the end of bountiful tier 8 delves.