I slackened my hardtail singlespeed by 1? and yes, I noticed the difference. I’ve also slackened a bike by 2? and that’s a really noticeable difference, though I also fitted a shorter stem to that to keep the steering sharp. I doubt you’d notice less than 1?.
Beneficial? Yes. More stable and better on steeps without hitting climbing ability by messing with the seat angle.
I actually changed my bikes partly because I was mostly riding a Ragley and found it quite hard to adapt to steeper angles on my other, less ridden, bikes. Kept over steering off the trail. I’ve ended up with a pretty slack 150mm/130mm Pace RC405 which I rather like, though it’s still a little steeper up front than the Ragley.