Windows 10 (But I suppose that problem is the same in all platforms)
When you use Blender2.80 default keymap with LeftMouse the keymap have a lot of hotkeys using "Click" event instead the "Press" Event. This make blender extremely laggy, specially in edit mesh. User can also don't select some elements if he move the mouse fast. The user experience is completely ruined for users.
- That event is used in a lot of hotkeys, I can see at least 30 with that event. Main hotkeys like select a vertex, context menu,... all that events are slower (a lot of slower).
- The problem exist in a lot of parts the keymap, not only in 3D view.
- I only see the problem in the mouse hotkeys, but I cannot be sure that keyboards don't have it.
- I didn't test other keymaps like right click or industry standard.
I mention @Campbell Barton (campbellbarton) because he was who decide to don't use the click event by this problem and work in the keymap, and @LazyDodo (LazyDodo) because he talk about this in devtalk forum.