Fighting a lot of these tribes must have been like boxing shadows. No towns, no cities, no plunderable resources. Only slaves and cattle.
There's been a ton of anachronistic crap written about it, that's for sure -- how they invented asymmetric warfare to fight the Romans, blah blah blah -- and yet the battles always saw the Romans vastly outnumbered, e.g. Caesar at Alesia, or Agricola at Mon Graupius, or the couple of understrength legions that annihilated Boudicca and her fellow mass-murderers. Caledonia always wound up behind some other frontiers in priority. Ireland was pacified and partly Romanized by trade, to the point that it was the first "country" to convert to Christianity, and the rest of Britain was converted by Irish evangelists.
Drone flight over Drumanagh site, Loughshinny, Co. Dublin