Space

Think of it as a scientific "what if" scenario. While there is, to the best of my limited knowledge, no reason to think such a thing is real - or even that it can be real - there's still much value in imagining it to be and proceeding accordingly. Having done so, one can then ask questions like "if it were real, what would the consequences be" (which can lead to theoretical insights that can later prove applicable to more practical things) or "what would we expect to see if observing such a thing" (which yields falsifiable tests, so we can go hunt in the data for instances of it). Another example of this sort of thing is the concept of a magnetic monopole.

Sometimes, these things prove to be potentially directly realizable (if not easily). One example of this is the Alcubierre drive. Initially, the concept was more or less discarded. Not because theory proved it unworkable, but because the required energy to achieve any significant effects was ludicrously impractical (mass/energy equivalent of Jupiter levels of impractical). Later developments drastically reduced the energy requirements to merely insane :)

It all just goes to show that we won't know what advances future developments might yield unless we try. Imagination is a wonderful thing.