Exercising using watts as metric

Around 750 watts is one horsepower. I'm not sure why you would want to use watts instead of what you're using now. Target? Sort of depends on the sort of training you're doing.

AFAIK only cyclists and rowers measure watts (power output) in training. Not sure if the measurement is meaningful for other sports.

Kayakers measure in watts on the erg too - pretty much any sport with ergs will use it at high levels (so wheelchair racing as well probably) It's useful if you have the scientific framework to make those numbers meaningful...

(ie: increasing wattage by X will result in Y speed gain. Assuming speed is your goal. If its something else, well then, not so much.)