To me, milestone xp/leveling actually frees up the party and the DM. It creates a specific goal oriented focus rather than a what can I do to gain more XP approach. Sure, some DMs and players who use xp can also focus on goals and avoid xp grind, but after using milestones, xp alone does not seem necessary. Also, with xp counting, sometimes it is hard for a DM to decide how much xp to grant. Here's an example: if a group runs away from a dragon that is worth 10,000 xp, I always find it difficult to judge how much xp they should gain. They may not have defeated the foe, but maybe running was the best option. If they fought and ran, they should gain some experience because they learned something about fighting dragons. Yet, if you award some xp, and they encounter the same dragon again, do they get full xp for defeating it or does the DM have to amortize the xp gain. Those types of situations bug me.
One of the knocks against milestone leveling is that players don't feel that their PCs are growing while they chase the next milestone. To combat this feeling, I like to divide each level into quarters and give out 1/4 milestones after 1-3 sessions when it seems appropriate. That way, they know if they are 1/2 way to leveling or 3/4, etc.