It's used in micro controllers, drones, some cameras etc. the whole point of my post is that apple should make a line of laptops that caters to people like artists, photographers, engineers, etc. They used to, and it was called the MacBook Pro.
A perfect example of this: I was recently at EDC, a massive music festival in Nevada, and one of our lighting displays had its controller stop working. I had my laptop with me, though, so I installed the control software on it. The comical part was that I had to plug I first a dongle to get USB, and then ANOTHER dongle to get Ethernet (controllers like this talk over artnet).
It was just really annoying. It felt like I was using a fashion device for work.
All will, the underlying technology is the same and the 'micro' just refers to the plastic shell; the adapter is just a spacer with electrical contacts.
Outside of phones, MicroSD isn't really used, and nobody uses MicroSD for transferring files.
SD cards are still the standard format for cameras, which are the main use case for SD card slots.