Homeguard is useful for defending inhibitors mostly. If the tower is down it's pretty easy to take an inhibitor, but homeguard essentially halves the time you have to leave for to heal at fountain and get back to defending.
I'm not sure how homeguard and alacrity would compare for running from fountain to fountain, but I feel the total time probably favors homeguard.
All in all, you get enchantments pretty late typically. Either because you finished most of your build or because of pressure at your base. In either event, you're going to be recalling to take advantage after an objective or running to defend an inhibitor, which homeguard gives the biggest benefit for.
It's worth seriously considering some other enchantments though for sure.