Thila was a mountainous planet with few colonies. It was largely ignored by the Empire, so the Rebels had placed a small outpost there. After the Battle of Yavin, Rebel High Command moved their operations there. While it was not meant to be a permanent base, it suited them well for a few months. When they decided to move on to Hoth, they rigged the base with bombs and leaked information about the base to the Imperials. When they came to investigate the trap was sprung.
Nobody important spent much time there.