It is important to remember to decrypt your microSD card before a Factory Data Reset, or if you are switching to a new phone. The data on your SD card will not be able to be read or decrypted after a reset or in another device. The only option to use the microSD card again is to wipe it completely.

Will I lose data if I decrypt my SD card?

When it is not the saved data on the card will be lost. That is how this security feature is designed to work... and so it does. With that said, if you properly decrypt with the same device, the data is not lost.

Is it good to encrypt your SD card?

The only real reason to encrypt your SD card in any phone is so that the only way to see what's on it is to unlock the screen. ... Some programs store their data on the SD card with encryption enabled, but encrypting the entire card is the only way to protect everything in one shot.