I almost always check luggage because:

1. I have limited upper body strength and an old hand injury that makes it very difficult to use that hand to lift even a moderately loaded rollaboard, or to manipulate other people's luggage to make room for mine in the overheads.

2. I have chronic anxiety about finding space for my carry-ons: I've been on too many trips where rollaboards have to be gate-checked anyway, and sometimes if I don't make sure I get on early, I can't even find space under the seat or in the overhead for my carryon backpack which contains my laptop, medications and other vital items (e.g., as in aisle seats with compressed underseat space, bulkheads, IFE equipment interfering with leg room/storage space etc.). I don't want to aggravate the lack of overhead space with yet another carryon.

3. Many of my trips are a combination of business and pleasure, or to climates where the weather is unpredictable, so I need a variety of clothing and shoe types (e.g., dress shoes and bulky hiking boots, business blazer and waterproof parka, etc.)

I think it's great if people can cram everything they need into the regulation sized carryons, but unfortunately I see way too many people bringing on things that are too big, or too many items at one time per pax.