In case you have problems to maximize completely the windows de GNOME, with a few small pixels left to cover ... well, I'll give you this brief but useful solution that took me a long time to discover.
All you have to do is verify that the Compiz window decorator is configured with the command "compiz-decorator –replace" and not with "gtk-window-decorator".
To change this configuration, open CompizConfig and select the item "Window Decoration". Then where it says "Command", I wrote "compiz-decorator –replace".
CompizConfig, using compiz-decorator
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