For most applications Unite will be enough, but for certain apps Rounded Window Corners helps a lot, in addition to Unite.
Besides the rounded corners, there's a Padding Clipping option in that extension which can clip/hide title bars, regardless if client side decorations or legacy.

This will work on Gnome 44.0 too!
You can hide specifically the Gnome Terminal title bar like so:
- In dconf-editor change
org.gnome.terminal.legacy.headerbar from Default to Custom value - false
- In terminal, right click anywhere and go to
Preferences, General and uncheck Show menubar by default
- Use
Unite for hiding the titlebar
At this point the titlebars should be entirely hidden, but if they are not for whatever reason, use Rounded Window Corners clipping:
Extensions, Rounded Window Corners, Padding to clip/hide the titlebar when minimized
You can use the clipping option per application, under the Custom tab.
The above two extensions will basically make it possible to hide the titlebar wherever you want.
Depending on the app though, in some cases you have to enable the legacy system title bars. One example is Google Chrome too. Note that the legacy title bar option is in Chrome settings:

Regarding Pixel Saver though, note that many report quite some performance issues or even "screen freezing".