If we were using DC, or AC with onlt resistance loads (IE: simple light bulbs), a watt and a volt-amp would be the same thing.
Unfortunately, we don't live in that kind of world. Large motors, lots of motors, variable spped controls, electronics, all sorts of things we use distort the wave form...and can fool our meters into thinking we're using more electricity than we actually are.
For the most part, this difference is of interest only to engineers. Most of us can get by equating one watt to one volt-amp.
