Some windows-specific professional software that cannot run on Linux.
Also, work-related stuff. I may be able to make a custom setup of Linux if I try hard enough, but when it comes to dealing with servers and VPNs it's a bit beyond me. Not to mention the time it takes to figure it out and set up.
Although, the more I hear about subscriptions from Microsoft the more I want to switch.
I'll add that you can always upgrade to 32Gb whenever you feel like it. It's the simplest upgrade you can make and takes only a couple minutes.
Realistically you'd want to upgrade to 32Gb after hitting the limit on 16Gb, this way you know for sure that it's needed. But if you're going from DDR4 to DDR5 then might as well just go 32Gb from the start.