That actually mostly depends on what you need it for.
When using SetUnitX and SetUnitY the unit can move (well he can get ordered to do so, he probably wont get too far) unless you pause him.
And SetUnitPosition of course isn't so slow (not enough to worry about it unless it's an extreme case) and can be used just fine.
Simply put SetUnitX and SetUnitY is "forced", the unit will get to where you want it no matter what even if it's outside map bounds or on the place of some other unit. SetUnitPosition is "safe" when it comes to this, if you want a footman placed on the position of some grunt then he will appear next to it.
I'm on a page about incorrect corrections, and spent the better part of like two hours trying to get someone to understand that -5^2 = -25, not 25, and then that post had comments get reposted because that group is self sustaining, and that person was in turn trying to explain what I just explained to them. And I'm taking that as a victory
I will be AFK for a couple of days you guys hold down the fort while I am gone. I will be checking in on my phone but that will severly limit me. Be back saturday!