Designing a game is a heavy task. There are gigantic teams that worked behind about every game you own, and if the credits are anything to go by, there can be hundreds of employees all working on the same video game. They all have their own tasks, and there are smaller teams working on every aspect of the game: The designs, the characters, the music, the programming, the level construction...
Now that I think of it, level construction is a pretty big task. Yeah, it is... Without an environment to roam, your player character wouldn't have anywhere to go. Therefore, the level designers are among the most important people in the making of a game. They don't just make the environment; usually they'll also be the ones choosing which enemy will be placed, where it will be placed, how it will act... Oh wait, that last one is made by the programmers. My mistake.
Anyway.. One problem with many games, especially platformers, is that at some point we're bound to run out of creativity in the level design. What do many level designers do, then? Easy: They copy bits of a preceding level, add more dangers, and voilà! You got your new level! That kind of thing has been seen in a lot of games, and mostly towards the end of those games. It's more obvious in platformers, especially those in which you can't really skip a level. It can happen in almost any game, actually; some places look damn similar but have just a few details changed here and there to make it different. Elements of the decor and copied and pasted, out of laziness or out of system limitations. It happens more often than you'd think. Are graphics repetitions such a big deal?
Well... Like I said not even three sentences ago, sometimes it was done because of technical limitations. In order to get everything to fit on the cartridge, it was much easier to just put the same background decoration on multiple places. This is really simple to see in the very first games. Take Asteroids, for example; always the same asteroids that come out towards your spaceship, and I think the smaller pieces don't even change when you blow them up. In the first Super Mario game, the same white cloud was repeated everywhere, and that same sprite was used, with a green color, to become bushes. Yeah.
But there's no such excuse for the games after technology let us go to 3D. The resemblances can be very noticeable this time around, because everything should - in theory - be different. You got to wonder is laziness is to blame. Is it? Well, it's kind of hard to say; as far as I know, I never went to a level designer and asked him if he was getting lazy at the job after the first seven worlds. I wouldn't sound too nice, either. But, what could be the other reasons that can justify those copied things?
Well, aside from technical limitations and laziness, copying the same designs can be a way to spare time. When you have absolutely everything to create in a game, ever single interior, every single patch of land, sometimes it's easier to just "copy-paste". Games are usually released on pre-determined dates, so sometimes the hurry to get te game out in due time can lead to this sort of thing being done.
Another reason would be to spare on complexity. Let's say you want to put the hero through a dungeion with a difficulty level that increases with every room; it would be simpler to just copy the floor itself, make the changes so that it leads somewhere else, and then change the enemies and traps in the room. You'll notice that this mostly happens with bonus challenges, the ones that you don't actually "need" to finish to beat the game. The train of thought probably goes like this: Why bother making ultra-detailed bonus worlds if some players won't even try them? Also, there's a possibility that the whole point is to make the player revisit past locations with an increased difficulty. Last but not least, maybe there's plot relevance to the fact that some rooms look the same, who knows?
Now, the cons to repeating graphics... Well, for starters, if it's a pretty big world and many locations look the same, yet have different purposes, it's easy to get lost. Say, as an example, that you need to get a number of items in the same level, but all the parts are so similar that you can'd find your way. Problematic, isn't it? Again, this kind of technique can be blamed on the level designers being lazy... When the place is an OBVIOUS copy-paste, then yes it's a problem again.
And actually, that's the big deal: If the graphics repetitions are obvious to the point that even a non-gamer could notice, there's a problem. Just changing the NPCs and a few details in each place is not always enough. I'd say that this technique is used best when you don't notice it too much. The problem is that after a while, it gets noticed, right?
So, are graphic repetitions such a big deal? Like I said, it depends on whether or not it was done out of laziness. In many cases, it was not, but it was because of elements out of the level designer's control (limitations) or really just to make sure that the places are similar, therefore bringing the player back to places he knows, except with differences to make it more difficult. It's not actually such a big deal. Though, it's still unnerving when the graphics are so obviously copied that you could blame laziness and it would be a reasonabkle defense...