It would be nice if somehow within the ACP, you could display the default value that XF ships with so that if we make a change, we can easily change it back to its default without resetting all settings to default.
That's what I typically do, but, it would be nice if you hovered, let's say, "Enable Multi-quote" in ACP > Setup Options > Messages, it said something like "Default: On (Checked)" as a tooltip.
Otherwise, each time one of us questions ourselves on a default setting, we fire up a demo to get an answer which takes about 5 minutes, and who knows how much resources are used to host that 3-day demo on XF for a simple answer, as asking on the forum would take longer.
I'm fine with using a demo to get the answer, it just seems like abuse to an extent when default settings could be somehow displayed or incorporated within the admin panel as described.
FWIW, "Revert to default" is potentially relatively simple to implement. "Show default" is not as simple, at least for many options. The checkbox example is pretty simple but there are also a bunch of very complex options that don't really work that way.
"Revert to default" wouldn't really have the UI challenge with the more complex options, though obviously it's not simultaneously viewable.
It just makes it easier to know the baseline of every default option because more forums are likely not to change from default until they grow. That way, we can fool around with it and return it to default without reinstalling it completely.
Getting back to growth, we know the baseline so we could easily grandfather the older user groups (if we're speaking revert to default like below) and set permissions for free members back to normal.
A "revert to default" option would be a happy medium as it's in styles. One could change things on a per-option basis and then remember which option it was prior (ie max conversation) and change it back if necessary.