It's both a good idea and a bad idea.
Good:
No one can get to your data. Even if someone steals your phone, the phone can be replaced. Your data is still safe. (NSA could probably get into it, but your average competent hacker can't.)
Bad"
If wither you forget the password, or something goes wrong with the decryption, say good bye - permanently - to your data, so you MUST keep backups of everything important at all times.
So if you have patent data or other company data that has to be kept safe, it's probably a good idea (although I wouldn't keep data like that on a phone to begin with). Otherwise - someone steals your friend's phone number? Is it worth losing all your data to safeguard that? (I consider it selling snow to Eskimos but convincing them it's special snow.)