If one wishes to attach a shooting sling, as opposed to a simple carry sling, then the worst place to attach it is to the barrel or anything directly attached to the barrel, such as the traditional FSB/Bayo lug point.
It's easy to deflect AR barrels up to and including the 20" HBAR barrel with a tight shooting sling. Deflecting the barrel with a shooting sling--or anything else, for that matter--will have definite and measurable adverse effects on the POI.
People using shooting slings attach the forward mounting point at a place where the sling not deflect the barrel. On the AR, that almost always means either a free-float handguard, or for Match shooters, a free-float tube concealed within the OEM handguards.
As long as the particular, chosen handguard meets one's needs, I see everything to gain from a free-float HG, and nothing to be gained by using non- free-floating HGs.
Before final purchase of what is advertised as a free-float HG, do some homework. Some seem to be much more rigid than others. Taking a tight sling on a very flexible Free-float HG could cause it to touch the barrel. Of course, this also depends on the barrel OD, and the ID of the FF HG.