Well, I am not the most experienced, but I did give myself a fright one year when the conditions were not best for the ewes (wet and cold) and the triplet mums nearly all got orf and/or mastitis as a result of the wee ones tugging and tugging trying to get more milk. The ewes - all of which were in good condition at lambing or there was no question of them rearing triplets - had free access to grass, more-or-less ad lib hard feed and ad-lib hay, they just simply couldn't make enough milk.
So since then I always always always offer top-up feeds to triplets - and if I think mum's short of milk but the lambs won't take a bottle (or the ewe won't let them) then I take a lamb off and hand-rear or foster it.
IMHO it's better to have a healthy mum with two good lambs, and a "pet", than a worn-down ewe with one good lamb and two weaker. In the latter case the outcome is often worse in terms of lambs produced and much worse for the ewe.