Whenever I feel like I want an add-on, it's really just because the built-in UI has something very lacking.

For example, I have a 3440x1440 yet I'm forced to use the same small area to display inventory in tabs as everyone else. I'm sure my CPU can handle something a lot more complex. Sometimes I also wish I had access to a list-form inventory. These can all be done easily via add-ons without impacting the baseline gameplay, as the official UI is always limited by the lowest spec the game is targeted to serve.

Other things like a list of daily/weekly to-do that is customizable. For example I do the weekly custom deliveries, but I don't bother myself with the beast tribe dailies nor the GC turn-ins. Or another player may only have GSM leveled and only care about the daily GC turn-in for GSM. A customizable to-do list will be able to display this information concisely, and maybe even create interactions that streamline the to-do process, such as clicking on the "Today's GSM turn-in is such-and-such item" to open up the crafting log at that specific item, ready to craft.

A lot of these small QoL improvements are being considered too insignificant and thus ignored by the developer. This is where the add-on community comes in.

So if I have to take a side, I'm on the side of allowing add-ons for these kind of features unrelated to combat. Either that, or expand the macro system a lot more to make such QoL improvements possible.