Have you taken a look at what CPU mining pays recently? It's a rounding error from zero. A modern Xeon does around 5-10 Mhash/core/s, while ASIC mining is measured in Ghash/s. Leave it on for a year and you'll mine an upper bound of 0.00004-0.00008 BTC/core, according to https://alloscomp.com/bitcoin/calculator (that's even discounting future difficulty increases, so is an optimistic estimate). That's 2-4 cents/core/year. If you have 1000 such cores going full-stop for the year, you'll net... $20-$40.