If you tick “Mix Down to one Audio File”, all of the selected tracks are played at the same time and rendered to a single track. This will allow any kind of bus compression or saturation/distortion to work like it should for example, retaining your mix’s balance. This is basically the same as rendering the group track itself.
Note that it’s possible to use Render in Place without any events selected. This gives you a few more options like the ability to disable the original track to save CPU.