The sexual intellectual(fornication knowest allest) thinks, Grout bags are very handy for any crooked joint that isn't tuck pointer friendly... Plastic throw away bags seem flow more constistantly than the reuseable M-town/Goldblatt bags w/ replaceable tips. And they "twist" with less elbow grease. Just as with plaster, cleanlinest is next to happiness, no dead mortar, or anything over 1/16th inch aggerate.
Fine sand, a little extra lime/cement, a teaspoon of dish soap will do wonders for plasticity and extend bag half-life times.
On anchored pre cast and stone raked/ unfilled joints, A little blue tape, almost liquid mortar in grout bags is fast, full, and clean. Or on jobs where the management "forgot" to order the colored mortar, filling the raked out joints.
Grout bags for me, are easier to use to completely fill hard to reach voids and repairing MEP damage to fire walls. Or when working in a completely finished room, the grout bag would be the delivery tool of choice.(cut tip at use point)