DPI

It does not decrease recoil.  I switched from 1600 to 800 then to 400 on both this game and OverWatch.

Lower DPI tends to remove the imperfections of your physical movement.  

eg.  If you try to draw a straight line with your mouse at 1600 vs 400 dpi the 400 dpi line will be straighter because it uses less input information.  That is the best way I can explain it.

if you think in terms of eDPI there is no difference in the number because you generally adjust ingame sens to accommodate the dpi change.  But people overlook the input information.

It is also most noticeable on flicking , while tracking may be easier on higher....but to me the higher dpi seems a waste because tracking is generally good enough at lower dpi also.

Playing on lower dpi is also mostly something arm aimers do.  I cannot vouch for how it feels with wrist aiming.  Like there may be no difference at the 2 dpi's doing the draw a straight line thing, if you are wrist aiming simply because of the physical distance you are moving the mouse.

Also keep in mind the ideal dpi can depend on resolution, if you play at 4k, 400 dpi or lower may not be the way to go....but I play at 1080p so 400 is fine for most shooters.