You should also be aware that the Filter Gramplet in the Sidebar is just the Gramplet that is most commonly used.
The other Gramplets (built-in and Third Party Add-on) provide many more alternatives to the basic features of Gramps. In most cases, add-ons were created because people felt something was too hard (maybe there were too many steps) or impossible with the Gramps core. (Many of the Add-ons were created by the core team members. So the 3rd-party is mostly about the feature not being included with the basic install package.)
For instance, this thread talks about using the Data Entry add-on to rough-in a tree:
