What's the purpose of reset controllers?

What's the purpose of reset controllers?

They seem to switch on/off something called reset lines by request of other drivers.

Why do SoCs need such a device?

(edit: also, is there some nice book which would answer this and similar SoC questions?)

The first time I came across a watchdog/reset was in an Anti-skid system for controlling truck brakes.

Anti-lock systems have to fail safe. If the program crashed it would not trip the watchdog. That would time out then make it reset. If it failed in a fashion that affected brakes, (e.g. solenoids on) it would blow it's own fuse.