With an internal 32GB memory ...you get maybe 25-29GB of space.
With an external SD slot ...you basically get unlimited memory.

Run out of space on your 25GBs of space? Too bad!
Want another movie, home video, TV Show, emulator games? Just slot in that extra microSD card that's stashed in your wallet!

I've been doing it for years, and its so much more practical than Dropbox and fixes the shortcomings of large files/many content/anemic internals.