The progress THz devices and methods have made suggest the use of the bandwidth for data transmission. THz data channels have great advantages. Even high atmospheric absorption can be bypassed by making use of transparency windows. There are several ways in which THz data transmission channels can be employed. We analyze possible applications of sub-THz data transmission channels, ground-to-ground (radio relay, mobile communications), ground-to-space (communication with space missions), space-to-space (communication deep space objects). The channel capacity has been estimated; drawbacks and advantages of each application have been considered. The channel capacity estimate will help determine the optimal use of THz communication channels and focus efforts on the most promising methods and devices. In particular, these data will be helpful for the choice of location for terrestrial transmission stations for the ground-to-space applications.