Why there is a "guest" acount in CSS?

When I install CSS in my machine, there is a guest acount with password “guest”.

Can I delete it?

Yes, of course. When booting livecd created user guest. During installation, users are transferred from the current system (in this case from the livecd). You can see the running:

cl-install -v -filter=user

Use the “-u none” to cancel the transfer of users:

cl-install -u none