I'm bringing this up because there seem to be mainly two kinds of games in this respect today: 1) "Let's remove the difficulties involved in making a game that encourages good backtracking by making the game linear enough to prevent it and adding regenerating health so that nobody has to go back," and 2) "And now, for MY entertainment, you shall replay the last five levels, AGAIN! MUHAHAHA!" I do not particularly like either of these, and I doubt that I am alone.
You see, backtracking is not something that you add to your game. It is something that emerges from the universe and mechanics you have created. That is not to say that you cannot intentionally create a universe and a set of mechanics that will encourage good backtracking, as you certainly can. I'm just saying that forcing the player to replay old levels or run back and forth is ridiculously monotonous and annoying. On the other hand, I like a game that leaves little goodies for people who want to explore, revisit, or comb over an area, and that is where persistent worlds come in.
Take System Shock 2, the game which is currently my "number one most favoritest game evar!" (which BTW is apparently a royal pain in the noggin to get running on a modern system.) The majority of this game takes place on a giant spaceship lost somewhere in deep space. At some point you might leave an object you want on the floor because you need the inventory space. Hours later, you can come back to that part of the ship and pick it up again. While you're there, you might check out a few little area's you didn't explore previously because you couldn't circumvent some obstacle or didn't notice them the first time. Making a game that will encourage players to backtrack and rewards them for it can be as simple as leaving some goodies around for explorers to find and allowing free run of most of your game world. There are maybe two to four places in System Shock 2 where the game prevents you from going back to earlier parts of the game. This not only encourages backtracking and exploration, but makes the game feel less like a set of levels or objectives to be played through in order(although it kind of is,) and more like a giant spaceship in which you are stranded, struggling to survive.
Of course, you can reward backtracking and exploration without an open world, but I feel that an open world is the best way to go in that area. If backtracking and exploration are not central to your game, making it more linear and finding other ways to encourage them in order to better serve the central parts of your game is just as admirable. The point is that while you shouldn't force backtracking on the player, throwing it out the airlock might not be the best idea either.