In theory it's a terrible idea, but for recreational use, reused wax is probably better than no wax at all.
For competition or best performance, you're going to be MUCH better off with new wax, not because the wax itself gets altered but because of all of the crap that it absorbs from your ski bases when it's applied warm and then scraped off. Wax cleans ski bases by pulling tons of dirt out of pore-like striations in your bases. Scraped wax contains a ton of that crap and putting it back on your skis isn't a great idea. Again though, I'd be willing to bet that reused wax is better than none at all or that re-used wax of the proper temp range is better than using brand new warm-weather wax on a cold day.
Miker is correct, racers used the waxing process to clean their bases, applying soft base wax multiple times until the base is clean.
Rather than try to reuse the shavings just done put so much on. I will quickly pass the wax block over the iron not to melt it, but to soften it and then crayon it on the base. Then I iron it in. Much less wax is used and much less scrapings. A large block will last my family two seasons.
You will find some of the best ski waxing tutorials or instructions on the Hertel ski wax website. Buy the big block from Hertel and you will have less concerns about cost. I see untrained ski tuners make several mistakes that both increase their costs and limit the durability of their wax jobs.
- using too much wax
- failing to get the wax fully liquified and forced into the pores of the base
- scraping while the wax is too warm. It takes more work to scrape and brush when the wax is cold, but allowing it to cool completely results in a longer lasting and better performing tune.
- reheating the wax to scrape it!