Well, as someone pointed out above, the world is a stage set. It really is a question of what you and the players need.
For an archetypal free-traders type game, I'd suggest you need a lot of detail so the players can get into the nitty-gritty of planning their journeys.
Somebody mentioned Arrakis. To be honest, if you look at it Arrakis is (excuse the term) stupid. An earth-sized planet, with 0% surface water and anaerobic animals weighing 1000s of tons that excrete oxygen. Doesn't spoil the book because the books aren't really about man vs a hostile physical environment. The books are about man vs a hostile political environment and the politics works well.
In Traveller terms, if the characters are representatives of the regional Duke/Lord their first question on planetfall is not going to be, "what's the star like? How far out from the star is this world? Can I carry guns? What's the best price for radioactive ores here?"
Their first question is going to be, "Where's the hotel? When's our appointment with the planetary ruler? Where's the bar?" In this case, planets probably could be described by a single phrase, because that's all that characters at that level would need.
OTOH, I definitely agree with the people who say, "nothing that is obviously impossible." We're there to play. We've already agreed on jump drives, ancients, intelligent aliens etc. We're disposed to accept your world. I'd say, give enough info to describe the world, but not too much or you risk destroying the believability.
Best example is the Force. We all accepted it, until they explained how it worked.
'course, I could be wrong.
