Overall I think it's worth it. I made a switch like this back in 2018, and it's worked very well for me. I ended up buying a new stock-config MBP15 because my previous laptop had a fatal failure and needed a quick replacement; A couple of months later I swapped to a maxed out i7 Mac mini and kept the laptop as a "backup" (in case the mini needed service) and for travelling; 5 years later (last year) I (mostly) replaced the mini with an upgraded M2 Studio, and still have the same laptop as backup/travel, which leads to one of the "downsides":

It makes for a conundrum when you finally need to replace the laptop. It isn't your primary use machine, so it becomes hard to justify costs of upgrading components on a replacement, but you need something that can do the core things your desktop does if you need to work while travelling (or the desktop is out of action).