Getting more info about new asteroids
In the game you will need to send scout ships to newly found asteroids to take some probes. To do so, the ship has to land on the surface and return to the home colony to bring back the results. That's the way to get knowledge of the available resources on other asteroids before you do a very expensive colony founding.
AI and procedural generated surfaces
Because every asteroid is randomly generated it is no easy task to make ship AI capable of finding a suitable landing spot and do the landing there - on an asteroid which is permanently moving.
The current AI is now capable of finding such spots, flying to a landing corridor and finally land on the surface.
Surface Landing has more benefits
You may find it disturbing or a waste of energy to have your ships orbiting the asteroid. For that reason you will be able to let your fleet land on your home asteroid to let them idle. They will not get repaired there and they will not be rearmed or recharged. But in the end they are able to get back to duty very fast in situations where you'll need their service very fast.
Surface is unprotected
If you get surprised by an asteroid-to-asteroid missile attack your ships on the surface will be very vulnerable to this attack. The good thing is you spare lots of Hangar Access Modules but you do so by making you vulnerable to different other sorts of attacks.