In practice space legs always ends up being a gimmick that takes dev time from the core mechanics. If you can get up and walk around then what you've got is a space ship game and another, usually totally separate, fps game. And since the main reason anyone is playing is the space ships you often end up with a severely underfleshed fps game, or a dev team that struggles to do both.

Elite's space legs was a clusterfuck. Now you can walk around and complete simple missions and get in firefights, but it barely interacts with the space flight layer. It doesn't even interact well with the go-kart layer, since there's no real way to balance the foot combat against the go kart combat against the ship combat, so there are arbitrary phony feeling targetting restrictions and damgage mitigation between layers. Want to use your super-powerful war ship to bombard the surface? There's a variety of mechanisms to prevent you doing that so you can't wipe out a settlement from orbit then land to collect the loot.