[Jaroslav Černý]

I ve seen some flashing lights as a way to put some pressure on you, personally i don't care but i can see how that could be annoying, and frankly a little low.

Otehrwise i use flash light in traffic ahead of time more as a "safety" attempt to just let people know a blue blag is coming cause people sometimes don't realize until it's actually blue flag which i think is a little late to show up on some tracks.

I may flash a car in front once to let them know I want to pass (blue flag) when it appears they do not see my turned on steady lights and are unaware of being flagged.
Or if people play dirty, pushing off track, colliding etc. but then they may just get the horn.
I always single flash when blue flaggers let me pass safely/well so they see my rear lights blink as a thank you.

Unlike most drivers my lights go from ON to OFF to ON, so it's a flash to black.

I ve seen some flashing lights as a way to put some pressure on you, personally i don't care but i can see how that could be annoying, and frankly a little low.

 

My question was especially about this topic

It can be done, doesn't work well anyway.

I think the only reason to flash lights is to indicate other drivers that you're about to lap them.

All other cases should be prohibited as flashing lights could affect game performance.

Yep.
It does not affect game performance unless the game is really crappy. What are you gonna do at night races when all cars have lights on? Run 10fps instead of 40fps? Hack the weather/time files so you have no night and no lights?

Its used a lot in GT racing. Its mostly just to distract the car in front in the hope he'll miss his braking point or apex. Its psychologically battling with the car in front to move his focus from whats in front of him, to whats behind him. The fact that there's a thread regarding it proves it works

Not really.
Anyone decent can see you even if you're 10 places down that you're climbing and catching up, about what lap you might catch up etc.
I find putting pressure  by presence works much better than trying to flash lights, it's more gonna distract you trying to flash lights than the person in front.

I know that in some leagues, for example in racedepartment, it is forbidden

For me, one solution is to deactivate the mirrors, if you are so annoying, you wont worry that I dont see you by the mirrors, try to pass me then... maybe you like the grass

And then you get penalties.
Kunos also thought of this, it's called forced rear view mirror.