What is the purpose of adding new file to the database? I'm fairly new at Microsoft SQL. I've seen many tutorials online on how to add a file to the database. What I still don't get is why?
You could


put huge archive data onto a big but slow drive
put structural information ("meta data") into its own file
put indexes etc. on a fast drive
put large readonly data (e.g. old legacy data) onto a SSD
set up a more intelligent backup strategy


I'm sure there's still more to add :-)