Horizon (Alaska) "AlaCart" planeside carry-on baggage service is not the usual gate check. Your AlaCart carry-on is deposited planeside on boarding, loaded into the cargo hold for the flight, and returned planeside on arrival. The specially tagged carry-on bags are the first off and rolled out on the tarmac within minutes of doors opening.
As someone noted, the bags are available planeside on the tarmac where jetways are not used. I believe it is PDX where jetways are used. In that case, its a bit congested deplaning in that passengers need to waite on one side of the jetway while the carry-on Ala Cart bags are brought up deposited on the otherside of the jetway. A bit congested, but with a small aircraft it works.
We use the Horizon AlaCart service except for our computer bags and fragile items. Ironically on one winter flight, my ski box and large gear duffle bag must have used up too much space in the cargo hold. The ground personnel had to bring in several of the AlaCart bags for storage in the overheads and under seats. Ironically, one of the AlaCart bags was my wife's Rick Steves Rolling Carry-on (the European airline legal one). I was lucky that Horizon didn't off load my skis.
I have flown on Horizon regionals with the opposite problem of too much luggage. I was on a late night lightly loaded flight where everyone had to sit in the back to accommodate the weight-balance requirements.