[AlexanderHowl]

Tide locked worlds are probably unlikely to be habitable by humans outside of the thin twilight zone (this is why orbital resonant worlds are better). The near side will always be covered by clouds due to evaporation and the near side will always dark, so photosynthesis is impossible without technological assistance. The difference in dayside and nightside will also not help.

Now, cooler worlds with tidelocking could potentially allow for more habitable area, but the nightside would be absolutely frozen in the case. With an average atmosphere, the dayside is +12% while the nightside is -20%, meaning that a 240K world would be 271K on dayside and 192K nightside. One problem though is that carbon dioxide snows at the nigh side temperature, so the biosphere would collapse, as there would be no carbon dioxide in the atmosphere to allow for photosynthesis.