SaaS, or "Software as a Service" is a trend in software companies to provide unlimited access to their product(s) for a recurring fee rather than a larger upfront costs for a standard perpetual license. Perhaps the most famous examples are Microsoft's Office 365 and Adobe's Creative Cloud.
Sample Library developer EastWest, makers of the EWQL series of sample libraries, has now jumped on this bandwagon.
It's tempting, I must admit. I could plug so many holes in my soundset right now if I signed-up, but I already pay for Adobe's SaaS and that shit really adds up over time.
I use several EastWest products already. In fact, the majority of my sounds are EastWest products, though. I'll definitely be thinking about this.