backless booster seatbelt clip question

[HIU8]

The clips that come with the backless boosters (to hold the shoulder belt down)----are they required or are they to use if the fit isn't great? I ask b/c my dad now has 2 harmony literiders to use (very occasionally) and I want to make sure he uses the clip if it needs to be used. FWIW, DS is 7 50.5 inches and 57 lbs. DD is 4 1/2, 46 inches and 45 lbs.

[Joolsplus2]

I didn't know the Harmony even came with one...(I never use them, they somehow end up tangled in my junk drawer, lol).
Nah, not necessary, unless it keeps the belt off their necks so that they are comfortable and don't put the belt behind their backs (so really, just for comfort).