I can't see a reason to group questions with the same voltage because many different types of circuits could be defined by either voltage.
We seem to have people relating this most to automotive applications due to tag descriptions, but if you look at the questions listed, they have automotive or battery applications or even solar. Someone could be designing a circuit with a 12V Vcc and throw that on the 12V tag.
I think these tags should be deleted. The questions in each tag are smattered with different unrelated subjects.
People should come up with a tag for their specific application, if its automotive, then they should use an automotive tag. If its a battery tag, then use the battery-charging or battery-operated tag.
I checked the 5V and 3.3V tags before I wrote this, but they actually have titles. However, if we were to change the 12V and 24V tags we should look at them also. At least the 3.3V and 5V tags have titles and seem to be associated with level shifting:
"Questions regarding 5V level signals, level-shifting, and circuits."
3.3V has the same thing:
"Questions regarding 3.3V level signals, level-shifting, and circuits"
instead of an ambiguous title like the 12V and 24V.
I don't know if I'd get rid of the 3.3V or 5V tags as they actually have a title (although I'd be much happier if we split those tags into something more meaningful, like 3.3V-CMOS or 5V-usb power ect) or just kill them also.
Again the voltage level has little to do with the question if you look at the other tags associated with the 3.3V and 5V tags.