What are the cons and pros of leaving Game Mode On constantly ?

So basically it was claimed that Game Mode previously found in game bar was a mean to give performance priority to games that are set to it , the theory behind it was vague and then there were posts it was about setting game priority to high while setting everything else priority to low including background apps and services .

Now on update 1809 Game Mode was moved to a new location in settings , became a general setting and is being set to on by default , now how would this impact windows usage in terms of cons and pros ? how are priorities being handled with it constantly on while no game is on or have they changed how it works as a whole ?

Game Mode barely gave performance boost, at least for me. There was like, around 1-3 FPS difference versus having it off.

Basically it's something that needs little attention.
Most people know that when running a game it is advisable to have the most resources and priorities allocated to that.

Unless you are a person leaving tons of junk(Applications, Apps, notifications, scheduled tasks etc) running in the background it will have next to zero effect whether it is On or Off.

If no game is running it will be Off, As soon as you start a game it will be On.

I don't remember what/when some scheduled tasks are going to run, so leaving Game Mode On makes sense.

The Game Bar used to be hidden in the Xbox App with Windows 8.1 and was subsequently moved to Windows 10 Settings in one of those version updates.

"I use Steam so I don't if it would do any good?"
I only have a couple of the other game clients, Uplay and Origin, in both settings are looked at and configured carefully.
They obviously use some extra resources if needed to run with a Game. No idea of the fine details.

ok first of all is it authentic to say game mode of 1809 can detect what's a game and what's not ? one version behind microsoft left it to manual toggle just because it couldn't figure all odds out .

second so its understandable its all about setting priorities so by leaving it on , foremost app/program whatever it is gets all priority ?

and on a side notice despite everybody believing its effect is vanilla , i could realize i get less hickups in 3d rendering of a game , by hickups i mean the moment rendering freezes to load a new asset so yes like @Faith said it does offer consistency