Not giving individual xp affects player choices by altering or even removing the risk-reward component.
If PCs get individual xp based on what they get involved in in-fiction then the players are free to choose whether or not to get their PCs involved, in full knowledge that choosing to get involved may have drawbacks (higher risk) but also benefits (more xp). This very intentionally dis-incentivizes hanging back, no matter the situation.
Milestone levelling or group xp actually incentivizes hanging back and letting others take the risk, given that you're all going to get the same reward anyway. On first glance, this seems utterly inane.
Of course, if one's game really doesn't have that much risk involved then it's all rather moot...along with IMO most of the fun of playing.