I generally pack quite light. On work trips I take only one personal-sized carry on (Red Oxx Mini Boss). I can fit a week's worth of clothes plus my laptop in this bag. I have no status anymore so I can't guarantee overhead space and I certainly don't want to be the reason my team gets held up on arrival waiting for my bag. I like having extremely little to worry about.
Domestically, my travels often involve connections. On regional jets. A carry-on of this size fits on pretty much any aircraft. More importantly, when things go pear-shaped, I don't have checked bags to worry about. This has saved me more than once. Most recently, I was able to switch *destinations* to avoid a storm only because I didn't have checked bags.
On long-haul travel, I still generally pack light (one full-sized carry-on plus a personal bag) but I'll often check my larger bag. Juggling more than that on trains and subways isn't pleasant.