If you have any apps on the SD card, encrypting it might cause the apps to stop working. I've been decrypting my SD card for the past 30 minutes and there's still a ways to go.
I am new to Android phones (finally got away from iPhone). I put a new 128 GB in my new galaxy s7 and started to encrypt it. It's been on "checking sd card" for well over 12 hours. I kept my card in exFAT......but that's WAY too long for something to encrypt. Any thoughts?