Being a fan of some science fiction genre pieces, I have seen my share of time travel movies and television shows. They usually take different approaches to the topic, with a unique twist here or there.
There's the situation when you can go back and time and see yourself, so basically there are two of you, one in the present and another from the future. Then there's the situation when you go back in time and there's only one of you, but you have your knowledge from the future. Also, if you travel forward, you go to the future, but your knowledge only extends up to the point in time when you traveled forward.
There's always talk of upsetting the timeline and changing history. You don't want to see yourself or tell yourself, "Hey, you're fat in the future, so you may want to think of taking better care of us." Other theories consider how the future changes with every iteration; every time it is relived, a new outcome arises from the chaotic assemblage of circumstance and random choice.
There's also another plot line that addresses a more outlandish concept, that there are myriad timelines, the number being limited by the number of possible choices in any given circumstance. All of these exist as threads, woven into the tapestry of time. We typically only experience one of these "threads", so we have no real awareness of these multiple realities. This has been a common theme on numerous Star Trek and Stargate episodes in most of their different series (Probably also in other sci-fi series, but I'm most familiar with these).
In my opinion, the concept of time travel is great for science fiction, yet it is just that: fiction. In our physical world, time is unidirectional and linear. It's like a burning fuse, the flame moving steadily in one direction, the fuse behind the flame spent. The fuse doesn't double back on itself or burn from both ends or anything weird like that.
The future doesn't yet exist, so you cannot go there. The past is spent and will never again exist in a time-and-space reality. Therefore, any concept of moving between present, past and future is pure fancy. Also, there are multiple choices at any given point in the present, but only one timeline exists, there being only room for one reality in it. In other words, I may have several choices about what I will eat for supper tonight, but come tomorrow morning, I will have made only one choice and only that choice will exist in reality.
The concept of multiple realities is a cool one, often pushed to ridiculous limits, made cooler because it allows each of us to imagine the possibility of ourselves living in other realities in entirely different circumstances. I've been there, speculating to foolish lengths about the "other me".
There's the Me that went to a different college to study engineering. I would end up married to someone else, as my wife in this reality met me at the college I went to in this reality which didn't have an engineering school.
There's also the Me that was more serious about music in his high school years. Frankly, I don't know what would have happened to this fellow, but I hope it would have lead to fame and fortune.
Then there's the Me that made different relationship choices in high school. This dude would probably be the most miserable of all, as the prospects available at that time wouldn't have led me down any path that would end well.
There are also outcomes and realities that I imagine arising from smaller, less significant decisions along the way. A different job here. Another choice there. A different church. More motivation and initiative, or perhaps less.
In these scenarios, we imagine ourselves most often as being happier, wealthier, more successful or with fewer flaws. We seldom consider that the other version of ourselves may be unhappier, poorer, a failure, or the biggest loser imaginable. That kind of speculation is not fun, so we avoid it.
Movies concerning time travel, specifically going backwards in time, usually allow the traveler the convenience of carrying his knowledge back with him. Also, the choices in that reality are fixed, i.e., if you don't upset the timeline with any new developments, things unfold exactly the same way every time. Change one outcome though, and the change cascades throughout time with often drastic results (the "Terminator" movies).
In my opinion, the most unique concept of time travel found in the movies is from The Butterfly Effect, starring Ashton Kutcher. Every time he traveled back in time to correct one thing, small changes in decisions yielded oftentimes drastic outcomes years down the road. The outcomes were random and unpredictable and differed drastically in each timeline. In this scenario, nothing could be gained from traveling back in time. Returning to the future, you would find everything different, and no outcome could be predicted or assumed based on any action in the past.
All of this is academic, as time travel is not possible, however it makes for some interesting musing. Just don't become one of those desperate souls like Uncle Rico, so dissatisfied with the present that happiness can only be found in the past.
