This concept is about exiting song select or anything where player currently is back to osu!logo after some time of inactivity:

Adding option to the settings to turn it on/off is needed in case of implementing it.
_ᴵˢ ᶦᵗ ᶜᵃˡˡᵉᵈ ˢᶜʳᵉᵉⁿˢᵃᵛᵉʳˀ_
Maybe they can make a black&white screensaver, like the one when you are closing osu!lazer:
For slow devices can be a nice feature I guess, or for just saving battery on laptops
Awesome idea!
Looks useless to me. Especially saving battery part of the idea since running Lazer is expensive regardless game state.

While saying screensaver i didn't meant actually saving battery but rather some cool feature that runs while you afk. Something that Gabixel proposed!
Eventually in the future osu!lazer could be more optimized for battery usage while screensaver is on.
That's true but theoretically, for laptops, a "black screen" should consume less power and save battery (as far as I know), not too much but can be a good solution (based on my idea for a black&white screensaver). But it's not necessarily just a "saving battery" option: for an AFK design can be nice too.
A good way to save power is to turn your laptop off. On most (non-OLED) screens black will consume more power (a good opportunity to go learn how an LCD screen works).
That said, we will be adding back an idle state similar to stable. The game should return to the large osu! logo (non-black) if left at the main menu. Undecided about other screens such as song select; that feels like something which would need to be a setting, or limited to when arcade mode is switched on.
TL;DR on LCD screens: there's a backlight shining at a constant brightness (regardless of whats on screen) and the pixels just control how much of that light can pass through. Therefore even displaying a pitch black fullscreen image doesn't affect energy consumption AT ALL since the blacklight is still shining.
But even if you have an AMOLED display (where pixels actually get turned off when set to black) the battery argument still makes no sense as you'd never leave a resource intensive game running idle on laptop that runs on battery in the first place. Further more this type of power saving is not the job of the game but of the computer (or the os).
Regarding idling in other screens, one option would be to eventually just go back to the main menu, and i agree this should definitely be togglable.
What is arcade mode?
I join the question
What is arcade mode?
You can find a couple of old videos here
https://www.youtube.com/user/peppyhax/videos
Locking thread as off-topic. If someone wishes to implement this, please go ahead by implementing as per how stable does it (menu should return to logo after around 10 seconds of idle).
Most helpful comment
A good way to save power is to turn your laptop off. On most (non-OLED) screens black will consume more power (a good opportunity to go learn how an LCD screen works).
That said, we will be adding back an idle state similar to stable. The game should return to the large osu! logo (non-black) if left at the main menu. Undecided about other screens such as song select; that feels like something which would need to be a setting, or limited to when arcade mode is switched on.