Even the smallest action has significance in this endless multiverse of ours. Travel back in time and you could profoundly change the future with tiny decisions. If you were to travel back in time millions of years ago and step on a bug, it could change the entire future of humanity. And the further back into the past you go, the bigger the future-changing impact becomes... So even a single insignificant ant will have significantly formed the future, billions of years from now, through his tiny actions.
Quantum theory suggests infinite probability. Going back in time changes nothing in the future.
You are traveling to a new universe that begins the moment you stop traveling through time.
The universe you travel to cannot have causal affect on the universe you came from, since you are no longer a part of the original universe.