XP (Career mode)?

[kingsofthevalley]

Completely oblivious as to what I'm supposed to be doing with XP. I thought it could be used as a supplement to evolution points to help unlock perk slots, offset evo point / cash use for new moves, etc (that made the most sense to me), but it doesn't appear to do anything in my career mode so what is it used for? I did notice a green "XP" bar in the lower right of my career hub that I cant seem to interact with and doesn't appear to offer any advantages during career matches. Thank you in advance!