I've got a powerful desktop computer, but I also have a 6 year old daughter and very little personal time. Grabbing the deck and playing alongside / with (for instance, both of us playing Minecraft, me on the deck, her on the PS5; or her playing on the PS5 while I play separately on the Deck) is a big thing. Also I have been emulating a lot, as she's stolen my switch so I can play on that. It's nice to be able to whack headphones in and game for 10 or 20 minutes in bed before sleep... Honestly, it broke and had to be RMA'd, and I missed it so much because the 'instant on' play for a few minutes is just so addictive...
I use it for emulation, (up to PS3 / Switch level works perfectly with a beta 3.5 OS with the SMT fixes), AAA gaming (Hogwarts legacy worked perfectly for the screen size at medium), old games, indie games, GamePass streaming, PS5 streaming...
It was a birthday present that I thought I'd use a reasonable amount. However, it's almost taken over my gaming time because even if I want to run something too powerful for the deck, I often don't want to sit infront of my home office PC (As I spend all day there working) and I can just stream from the PC using SteamLink / Sunlight:Moonlight... It's basically only when I want to play at full-screen 4K and have a few hours to myself I bother to game on the PC.