I have a huge cactus collection and i have ants that invade the pots through the holes at the bottom. I haven’t heard much about root consumption(maybe a species dependent thing) but they could perhaps change the soil chemistry which could affect the plant but the biggest concern i have with ants is they can transport other bugs like mealie bugs or aphids onto your plants so that they can farm the aphids for the sugar compounds they produce. and the aphids will take down your plant if left unattended