When you are out and about with your laptop you are usually making your DNS calls to the local router which many view as a big privacy concern. Even if you use something like google's 8.8.8.8 and 8.8.4.4 public DNS servers as your defaults the traffic is easily sniffable.
When you connect to any site, your browser sends the domain in clear-text (even for HTTPS - see SNI). The only way to avoid this is to use a VPN, but then you can route regular DNS over that too.
