To be able to change fonts, color fonts, change background colors of cells and columns etc should be a very basic function that should be included for a multitude of reasons (I bet each user probably has his own reason), its even so basic that justifying it with a reason seems pointless. I even have more customability choices with the text I write in this little free chat ui here then I have in a pro version of an advanced webbased software that costs 20$ a month. But since you asked for a reason, mine is to make certain cells stand out from the others, for example I am making a list of all our products, certain things might have issues, like the price is wrong, or the measurements are wrong etc, and a very simple, quick and effective way to make these issues stand out is to simply color the cells that contain that information red so that my employees will be able to notice it straight away, once they have fixed the issue they can simply color the cell green and I will know that this problem has been solved.
You’ve got Views for that, even Groups could work. Easier than manually coloring records.
Manually coloring records (I actually mean cells…) would be a lot of work indeed. Personally I use conditionally formatting all the time, and I wish Airtable would have a solution to achieve that.