Windows XP: Consequences of setting a password for an account

"The other consequence, is that your account can be used to connect to the computer over the network. By default, Windows XP (and later), accounts with no password cannot be used to access the computer from the network. So it closes off any external attacks; in that way it is better than an account with a weak password.

For that reason it is sometimes recommended to have user accounts with no password at all.

As for why I can see a number of reasons:

Windows XP was the transition for mainstream users from Win 9x that didn't have any passwords.
Some people could be confused by having a password (or the whole idea of accounts), forgetting the password, etc.
The computer doesn't need a password. That is there is nothing important enough to protect. (And due to the network lockout, it can only be accessed physically. If that's a home machine it means that the attacker is already in your house)"

Scheduled Tasks can run just fine on an account without a password. When you're prompted for the password, press Enter.