It's really a question of strategy versus tactics. Do you plan things out ahead, gather data on the probabilities and possible outcomes beforehand (strategy), or do you just dive in head-first and deal with things as they're thrown at you (tactics)? Arbitrary encounters aren't popular with the strategic players, but keep things interesting for the tactical guys. The optimal balance between the two is something that will differ for each player, so the biggest win will probably be to assess where that balance is based on the player's actions and adjust your randomness accordingly.
I think it's all related to the kind of enjoyment the player is looking for - a quick thrill, or a longer more sustaining experience? I could try and draw the same parallel with something like continuity in a comic - you've got Gary Larson's single panels, you've got Penny Arcade's three-panel-with-occasional-cross-strip-continuity, you've got Neil Gaiman's Sandman stories that fill a book each. The first requires a minimum of time investment from the reader, but the value gained - integral(additional entertainment value) - is smaller than the last (which has been known to keep me engaged for hours on end).