In the season 4 episodes "Wolves and a Door" and "A World Between Worlds," it is revealed that the Emperor ordered the base on Lothal in order to access its Jedi Temple. The Lothal Jedi Temple is one of the gateways to the World Between Worlds, a mystical plane within the Force that has various pathways to different areas of time and space.
According to the Wookieepedia article on the World Between Worlds:
Darth Sidious, ruler of the Galactic Empire, sought to enter the world between worlds, as gaining access would give him unimaginable power, and as Minister Veris Hydan believed, control of the universe.
This explains why Palpatine ordered the base on Lothal, because he believes it would give him unlimited power.
Additionally, the TIE Defender was developed exclusively on Lothal. Cheaper and possibly more efficient than funding the Death Star, Grand Admiral Thrawn utilized Lothal's extensive fuel depots to fuel the project he developed. Several of the prototype defenders were built, but Governor Arihnda Pryce's destruction of the fuel depots forced the project to be shut down indefinitely.
Wookieepedia article on World between worlds
Wookieepedia article on TIE Defender