It’s useful; I use it most of the time. The previous Yaris didn’t have it, and it would crawl forward on the level at walking pace on taking my foot off the brake. As long as you don’t mind the brake lights being on display when it’s in “Hold”, it’s useful in traffic queues.
Useful for urban driving, where you're constantly stopping in traffic and at junctions. It's basically just an automatic handbrake. I generally don't have it on when using adaptive cruise control (motorways, dual carriageways, etc), because the adaptive cruise control will do pretty much the same thing - as long it has stopped the car rather than you braking.