There are a couple ways in which its useful to me.
First is when I just want a windows-esque interface with lots of floating windows. Especially for Office apps, because they also start looking more like their Windows counterparts. Through tablet itself it may not see that much use, but when connected to an external monitor it’s really nice.
And second is when you want to separate your daily routine with work. Because Dex is visually very different you can use it as a sort of “focus mode”, which works great for me personally.
Although whenever I need to do something more demanding than Excel I tend to just remote to my home PC.
I should also mention that I am studying at a uni, so unless I need to work away from home specifically and if it’s not related to studying then Dex doesn’t get used much and I just stick to conventional means of consuming media.
But I do know people who straight up replaced their PCs with that thing, depends on your use-case scenario.