When ds was a baby and I used the carrier, I left the handle up. As he got older and he slept less, I left the handle down to make it easier to get him in and out. (He was preemie and slept a ton, the infant carrier was a lifesaver to not be waking him up.)
As for what I tell parents, I tell them what positions are approved and leave the choice up to them.
My instructor was very against leaving the handle up even on seats that allowed it, but that was because she was a first responder and had been to a collision where a baby died due to being in a seat that the handle had been left up on when the manufacturer didn't allow it. It was the handle breaking that injured the baby and caused her death. I don't think she knows about combi seats though... they're not very common to see around here.
At our seat checks if it can be up or down: I explain to parents that it can be up at the first click or down at the bottom 2 clicks for example with the new gracos. I also explain that it can't be around the top of the shell & that they will see this misuse a lot with this graco seat & they can remind their other mama friends to read their manuals. I usually leave the handle in the bottom position at the end of the check, because we recommend riding next to baby for the first few trips & they will be able to see baby better without the handle in the way. And get in the habit of not leaving it along the shell.
Just so that you know, the 2 clicks back is only for the snugride. The SS1 only has 4 handle positions. All except for B are allowed in the car, whereas the snugride has 5 and positions b, and c - the one along the top edge of the seat, aren't allowed. With the SS1 though, the position that's along the top edge of the shell is position C and it's an allowed position. :thumbsup: