On the remote side of a connection you can use either Host or Agent. Their features mostly overlap and in many cases you can use either. In some scenarios, however, using Host may be more appropriate than using Agent, and vice versa.
The Host is a persistent remote module. It runs as a system service and starts automatically with Windows. This lets you establish a remote connection with an unattended remote computer which is the main reason behind using the Host, although the Host is also suitable for attended remote support. If you need to access “headless” machines (i.e. those without a monitor plugged in) then using the Host is the only option.
You can tell if the Host is running by looking at the system tray area of the Windows task bar. If the Host is installed on the PC and is running, there is the Host icon in the system tray: