Speaking about buttons used in People, Places, Sources to group or ungroup list view, as :
Shouldn’t these two buttons be combined into a single group/ungroup toggle button ?
If it’s a bad idea they need, at any rate, to preserve their selected state (it isn’t the case currently when you click again on a selected one).
Best regards.
There are separate view mode buttons because these are entirely different modules and not inverse functions. (They don’t share sidebar or bottom bar settings. They both chose to follow the changing focus of the Active Person.)
The anticipation is that someone will come up with alternate modes of organizing people.
Someone might decide to write a Group by Name that uses phonics (perhaps by Soundex or a competing system). Or by lineage without dependence on the Surname crutch.
Or by genetics groupings, whether genotype or phenotype.
Maybe someone will devise an entirely non-tabular organization.
To expand on @emyoulation’s comment.
The same formatting is used under Charts and Geography. These have more than two views. Each view in the subset has all the icons to switch to another view.
Thank you @emyoulation and @DaveSch for your deep explanations.
All the buttons you mentioned should keep their “selected” state when (are selected and) you click on them again.
Best regards.
Thanks for the ego stroke 
(Now I have to make sure to deflate it again!)
Yes, there seem to be some places where View Mode selections and configurations do not persist.
There are so many Views (and Modes of those Views) that the test grid intimidated me. It wasn’t enough of an irritant (to me) to justify designing a structured test plan, executing it and then writing the enhancement request.