When we transmit electricity down miles of wires & cables, we lose a big percentage of it. If there could ever be superconducting transmission lines, people all over the world would need to generate less electricity, which would really be good for our environments.
As others have already mentioned, there are various possible reasons room temperature superconductivity may not necessarily be quite so amazing as often thought. When it comes to power transmission there is a very important point - superconductors have zero DC resistance, they do not have zero AC impedance. If we switched to DC power lines and kept the current below the critical current, we could eliminate most power loss. With existing grids, however, we could not simply replace the wires with superconducting ones and expect to see power loss disappear. In fact, we could easily end with things being significantly worse.
Another important point is that all known high temperature superconductors are ceramics. This makes them rather difficult to make into things like wires, since instead of just stretching them out as is done with metals, you have to go through rather complicated, expensive processes that still don't result in wires anywhere near as easy to work with as metal ones. They also have a high failure rate since any flaws anywhere in the process (which usually involves powder being heating in a mould and can easily introduce impurities, air bubbles, and so on) can result in the whole length of wire being useless. Obviously this is far from ideal when you want to make large amounts of cheap, reliable wire covering hundreds of kilometres.
The point being that even assuming we discover a cheap, easily produced room temperature superconductor, it will not necessarily be cost effective to actually use it in many situations where it might seem useful. For example, it could easily be cheaper to build a few more power plants to cover power losses than to produce and maintain an entire national grid of superconducting power cables. There would certainly be some uses for it. After all, superconductors can be useful for enough for us to go to crazy lengths involving liquid helium to use them. But just as superconductors, followed by high temperature superconductors, did not revolutionise the whole world, there is no guarantee room temperature ones would either.