With some older mouses, you could change the "angle" in a control setting so that if you wanted the mouse could point northwest (or northeast) but screen "up and down" still corresponded to an up/down motion on the mousepad.
With some "modern" mouses, it happens automatically - although I hadn't actually noticed that mine does an automatic compensation until very recently. Especially if it happens without changing a setting, this eliminates the need for a fixed "wrist cock" that might stress the joint(s), and allows you to get some "wiggle" into mousing.
(The three that I checked just now all allow up to about 40 degrees of "cockiness" and still compensate accurately, but all three are both "wireless" and "optical" and I'm not sure which feature allows the mouse to know when to be a crab instead of a mouse.