I use one every gig (mounted to my HH). I don't need/rely on it as much as I used to but it's still at every gig. I program. On 3-4 hour gigs, 30 program positions isn't enough for all songs. So, I program either the songs that I start or the ones that other musicians start and we often have tempo issues with. So then, on my set let, I'll have the program spot number after the songs I've put in that program position. See attached for example.
Instead of a click, I also used LiveBPM on my phone, also mounted to my HH, to monitor tempo just so things stay where they need to be.