The whole point of a loose footed main is to allow for more sail adjustment. So, I'm talking about any sailing situation where that adjustment is important, as is particularly the case in upwind/downwind sailing. Downwind I relax the outhaul to let the sail belly out. Upwind, with a loose footed main, there is no bolt rope to hold the foot on the boom. The outhaul is the only mechanism for keeping the foot tight and in a blow it needs as tight as possible. If you can't get it tight enough you will get a lot of drag, and heel, out of your mainsail. Hence the need for a strong out haul. Also, if you're going to reef a loose footed main, you need to get the foot really tight or you're going to end up with a mess. If you wait too long to reef, and the sail is all loaded up, a strong outhaul is essential.
Different strokes for different boats I imagine. For fixed bearing sailing, set it leave it and just steer, then main sail adjustment may not be particularly important. But we don't see such sailing on the Columbia River and I suspect other river sailing situations are similar. Also, my experience is with a big main rig (and would certainly be true for a fractional rig). For big headsail small main, IOR style rigs, mainsail adjustment may be less important. Just speculating, I really don't know.