There is no salary floor. But they have to pay a certain amount to their roster. If they don't reach that amount they must pay the players on the roster the extra. So they were going to spend most of that money anyway. This way they spend it while acquiring Rush and 4 draft picks.
There is a salary floor, and it is 90% of the CAP this year. https://www.cbafaq.com/salarycap.htm#Q15
So, while Infection poster is right: 20 mil is real money, we had to spend it ANYWAY! We spent it on expiring contracts of back-up scrubs, hence ensuring our young core gets to start and play good minutes and got draft picks in the process. This is not a bad financial move at all.