This is quick guide how to get rid of title bars in Plasma 5. You will require mouse or touchpad with middle-click function.

In pursuit for screen space I've found really nice option to disable title bar and not loose border:
https://www.reddit.com/r/unixporn/comme ... _plasma_5/

System Settings -> Application Style -> Window Decorations
Click one of the themes context menu icon
Window Specific Overrides -> Add
Click "Hide window title bar"
Use .* for the regular expression to match all windows

Now little tweak:

System Settings -> Application Style -> Window Decorations
There is border size at the bottom, change it to small

But how to maximize/minimize/restore window?

Navigate: System Settings -> Window Management -> Window Behavior
For Window Content, Title Bar and Border set:
Modifier Key to Meta (as Alt will conflict with most of apps: viewtopic.php?f=83&t=139423 )
Left click to Move
Middle Click to Resize
Right Click to Minimize
Wheel to Maximize/restore

You will get such nice windows:

Thank you for the interesting exercise/tip. I like the idea of retrieving some screen space, but not the idea of a "feature" only known by the user -- after all, I may wake up some day and not remember the "feature" operating procedure. Perhaps a mouse hover could retrieve the Title Bar; thus, allowing me to use the features that it offers.

I'm giving it another try -- it does help to unclutter the workspace. Notice that once you apply to remove the Title Bar, the Theme identifier vanishes in the Windows Decorations settings.