Liquid wax trades some durability for speed and convenience. There is no iron, no scraping and no cooling wait: wipe or spray it on, let it dry, buff it out, and the ski is ready in minutes.
That makes it useful in two situations: a quick refresh between runs or at the top of a course, and travel, where hauling an iron and bench is not practical.
It is not a replacement for an ironed-in wax job. Liquid sits on the surface rather than soaking into the base, so it wears off in a few runs rather than a few days. Treat it as a top-up on a base that is already prepared, not as the preparation itself.