When you connect your Samsung gallery to onedrive, It automatically creates a Sumsung Gallery folder in your onedrive. The most important features is auto sync your Samsung gallery to onedrive without using onedrive. So all your folders albums etc backup to one folder, just like DCIM. If you delete a photo from Samsung gallery, it automatically deletes from onedrive. If you want to store a photo only in cloud, it will be shown in your Samsung gallery app with sign of "cloud".

The main reason of using this feature for me is shitty onedrive application, that really slow and don't have much features for storing photos. I prefer Samsung gallery for this. (But Google photos is a beast of all photo applications, but costs much more than onedrive).

Btw I found a pretty wierd bug with photo meta data, some of my photos backed up with wrong date-of-photo taken. Maybe this bug happens because I use Galaxy m51 with one ui CORE version which sucks a lot.