I didn't know that you can do this!

On important stuff you want to keep , files music,photos never hurts to have 2 or 3 backup from cloud,another sd card , or another source.. I never trust just one
 
i have some rarely used apps on the SD card, what happens to them on the sd card?

Biggest concern is performance, when adoptable storage became a thing a few years ago Samsung was against it because it negatively impacts performance and can give the user the opinion their phone is slow or under performing.

Similar to a PC, if you've got an SSD with plenty of storage, why install programs on an old mechanical HDD?
 
On important stuff you want to keep , files music,photos never hurts to have 2 or 3 backup from cloud,another sd card , or another source.. I never trust just one
This is extremely important. There are many people who do not back up their pictures, and then they lose them forever if the SD card fails.
 
If you have a high quality SD card, Samsung's best 64 GB for instance, the main issue is that you have to move the app back to the SD card every time it updates. Time consuming if you use alot of apps that way.
i have some rarely used apps on the SD card, what happens to them on the sd card?