Encrypt phone - should I try it?

I recently wandered in the security settings of my device, and found the "encrypt phone" setting. If I understand correctly, it'll ask me for a PIN in order to unlock my phone every time I turn it on.

Has anyone tried it? Will it make the phone any slower? This is obviously non reversible (a factory reset is required to return it to previous state), so are there any negative aspects I should be aware of? I'm not a security freak, but I don't mind putting a 4-digit pin every time I open the phone, if the advantages outweigh the disadvantages.