If I set my laptop to sleep on lid close, everything goes haywire. On waking, it won't connect to wifi or even show the connections window. Sometimes I can't even get the main menu to come up. If it does and I open an app, it might do nothing or it might open the app window but it's filled with my desktop background. Sometimes there are other weird graphical glitches, too. I can't reboot from this state. If I try, it hangs on the Kubuntu splash screen. If I shut down from this state with REISUO (because it won't shut down proplerly, either) I can only boot from bios menu. If I try to suspend from the start menu and not by closing the lid, I get things like this:
Freezing of tasks failed after 20.12 seconds (12 tasks refusing to freeze, qu-busy
then it will automatically come back to the desktop in the above state without any input from me. If I uncheck everything in power management and never use suspend, everything seems to work properly again on reboot.

That's not very convenient for a laptop, though.

Lenovo Z70 8G ram, Nvidia GeForce 840M using the Nvidia 390 drivers