Where would we be without GNOME Tweak Tool and would you even use GNOME 3 without it? MY guess is that a lot of you guys probably wouldn't be using GNOME 3 because it was painful without it I can tell you.
Extensions to the rescue I hear you say, no, sorry, they break in every new version of GNOME 3, just like GNOME Shell themes, just like GTK3 themes. Remember the good old days when you could drag and drop GTK themes, icon themes into the theme window? Oh, those where the days when Linux desktops were more customisable than Windows or OS X by default.
Now days we cannot change anything easy without our hero the GNOME Tweak Tool. It's our saviour of easy customisation that fights for the users and defends us from those Windows and OS X users, who laugh at us because we cannot change our font sizes, colours, cursors and themes easier than those evil proprietary OS's.