So I’ve been learning this myself and have watched far too many videos on the topic. Essentially we use a figure called eDPI (effective dots per inch). We get this figure by multiplying the DPI of the mouse with the sensitivity in the game.
Most players play with somewhere between 4000 and 8000 eDPI. Most pro players play with somewhere between 4000 and 6000. The larger your mouse mat is, the lower you can afford to have your eDPI because you can just move it more to compensate. Pro players use their arm, wrist and fingers to aim in different situations, and a low eDPI allows the fine aiming with wrist and fingers whilst having such large mousemats allows you to lock your wrist and move your arm crazy distances.
Now, many of us don’t have massive mousemats and might not be used to aiming like this, and some of us genuinely play better at higher eDPI. It is of note that within pro players, the more DPS roles a player fills, the closer to 4000 (or even 3000!), and the more Tank and Support roles, the closer to 5000 or 6000. If aim isn’t as important but being able to turn around and swing your hammer/mace is or being able to 180 and speedboost/guardian angel away is, maybe consider this.
So if the lower eDPI is better, why do mice allow such high settings? The answer in Overwatch is screen tearing, although in RTS games you really do want crazy high DPI. Now I’m not a techie guy, but for some reason having a high DPI and a low sensitivity results in less screen tearing than a low DPI and a high sensitivity. Although the eDPI works out the same, your aim will be better if you can circumvent the screen tearing.
If you don’t know what the best eDPI is for you, I recommend a technique I found online. Without warming up, set your in game sensitivity to 10, your mouse DPI to 500 (giving you an eDPI of 5000)* and in the training range, strafe while trying to keep your crosshair on the head of a static training bot at a variety of ranges, but focus on the most effective ranges of your main characters. Then change sensitivity to 15, repeat, and again at 5 sensitivity. Which one felt better, 5 or 15? If it was 5, try again at 2.5 and 7.5, or 12.5 and 17.5 if 15 was better. Keep doing this until you find a sweetspot where every change is worse than what you had.
Congrats! You’ve found your perfect eDPI! Now, if you’re tired or on caffeine at the time it might be different so try and repeat this test without warming up and when you’re at a baseline state. But yeah, there you have it. Lets say your sweet spot works out at 4750 eDPI like mine was, do what I did and set your mouse to that exact figure, then change in game sensitivity to 1. Problem with this is the mouse will be wicked fast in menus but I use a DPI switch to change to 2000 so I can manoeuvre the menus.
I hope this helps, I’d played with a controller my whole life and just got a decent mouse and mousemat and this has helped perfectly.
*I got these pro figures from a Jayne Q&A, and if you don’t know he’s the coach for Dallas Fuel and team Canada. A great streamer and full of advice for scrubs like me. The techniques I got from a personal coach named Love, and after getting a new mousemat my ideal settings have changed. If you only have a small mousemat, rather than starting at 5000 eDPI, try and find the setting whereby moving from as far left as you can to as far right performs a 360, and start from there, going 50% up and down of that figure and narrowing it down as such. You don’t want a perfect eDPI that doesn’t allow you to turn around without lifting the mouse.