I guess you're talking about the current stable version of godot (2.1.4).
The profiler (+the other tabs like "Monitor") helps to identify actual or potential performance problems in your application.
You'll start it while the app is running and you can select different topic which can be added to the graph.
You'll see the frame rate and also how much cpu physics or script functions use depending on the current state of the game. You can also do changes in the node tree of scene files and watch the performance changes. I.e. you can hide certain groups/nodes and watch if there's an impact on the frame rate.
If you develop for android, you can also link the device via usb & network, set up the editor and can then do the same on a mobile device (profiler node-tree on pc, while the app is running on the mobile device). It sometimes helps to not debug on the best performing device :)
Remote debugging/profiling may not be the simplest to set up but is extremely helpful+comfortable if it works. It helped me to identify some performance problems caused by 3d physics (custom 3d collision meshes vs. 3d areas caused some performance hits).