I've worked with track panels in South Africa - a piece of track a few metres long (can't remember exactly how long) with steel sleepers, which can be moved into place and then bolted to the next piece. In our case we lifted old disused track in panels and relaid it in our depot. It only really works with old-fashioned track where lengths are bolted together, not with continuously-welded track, so I doubt whether anybody would want to use it for major running lines, only in sidings perhaps.
Throughout the world nowadays I believe most running lines are continuously welded, and track is laid by specially designed works trains where the whole procedure is automated. It's much quicker, safer and cost-effective than using track panels, produces a better end result, and uses less labour.