If you are planning to telnet into your router remotely, you need to add an enable password or enable secret password, or the router will not allow you to go to enable mode. Of course, it goes without saying that adding an enable password is always a good thing

! Enable service password-encryption if it isn't already.
service password-encryption
! Here is our enable password, which is ok
! but not too secure.
enable password 7 141B171F01012325
! Here is our enable secret, much better.
enable secret 5 $1$99Jc$dxVXUkwMM3Edvj7f0SUrL/

Don't forget that "enable secret" overrides the "enable" password. Just be safe and use the enable secret command. The enable secret uses a better encryption method to encode the password.