Why have I to enable second passphrase? Is it not safe enough?
First of all: It's as safe, as your machine is. Nothing can protect your passphrase, if you execute a trojan on your machine.
The first passphrase is used to get
into your account. To use the LSK of the account (voting, send LSK,...), you need the second passphrase (if enabled). It's "safer", yes. Anyways, if your machine is compromised, both passphrases may be catched by the intruder. I reccomend to use a password manger like KeePass. This way you are able to copy/paste your passphrases (which will remain only 12 seconds in your clipboard).
P.S.: You should write down all passphrases on a sheet, in case of hardware issues.