The problem with settling my GGs is that I always get the first few before I have the tech for the military academy (Education). That leaves the only choices as the military instructor (+2 exp) and the Warlord (unit). Of course, the military instructor wins out 9 times out of 10.
Rather than attach a Warlord to the best unit, sometimes I will attach him to the early Warrior that maxed out experience killing barbs (@10xp) so he can upgrade for free to Maceman or better. Otherwise, he would just spend most of the game being a happiness reducer deep in my territory. It's a cheap way to get that one extra combat unit (it's cheaper to replace a defensive unit than a combat unit). You never know, it might be that unit that takes that city one turn earlier than otherwise, saving someone else who would have had to suicide into the reinforcements (not to mention the power points you get from the more modern unit). It doesn't make as much sense if the low tech unit didn't have experience of course.
It's giving up a military instructor or academy, though, so it's more for fun than a real advantage.