Hi everyone,
I just switched from Unity to KDE on freshly installed Ubuntu 16.04 and noticed that when I reopen an app its window size and position is different from the ones it had before closing and returns to some defaults - bottom right corner, about a quarter of the screen. How can I force the apps to save window placement on close?

Hi !
Welcome to the KDE side.

The KDE is using, as default, the 'smart' window placement.
KDE System Settings > Window Management > Window Behavior (Advanced tab).

More information can be found from the 'What's this' (1) and the Window Behavior doc (2):



The placement policy can be overruled by the Window rules.
KDE System Settings > Window Management > Window Rules.
or/and right click on the title-bar of any window:



More information can be found from the 'Help'.
The KDE Userbase has step-by-step examples: https://userbase.kde.org/KWin_Rules