The SaaS, a.k.a. Software as a Service, business model has become unfortunately common these days. Applications that you used to be able to buy a copy of outright, such as Microsoft Word or Adobe Photoshop, are now available exclusively on a subscription basis, with no option other than to subscribe or switch to a different product. While some customers may not mind, it's hard for the canny or cynical user to avoid noticing the pattern: software is converted into a service solely so that users have to keep paying for it, or risk losing access to everything they use the product for.
Nevertheless, there are real use cases for services. Even ignoring things like social networks that only function if users can connect to a well-maintained, always functioning remote server, there are numerous industrial processes that work best at scale, and trying to be completely independent of greater society is a fool's errand. Public transportation, insurance, and even food are essentially "services" in the modern world, although one may not have a subscription per se.
This all leads me to what is becoming my rule of thumb: SaaS should stand for Service as a Software, not the other way around.
In other words, if you are truly developing a service that will add value due to being a service, and you use software to deliver said service, you are fine. To name some examples, VPS providers, social media platforms, and online banking systems all fall into this category — they provide something that can only be effectively implemented as a service, and the software is just part of the delivery (where previous generations might have had to use the telephone or go to a physical location).
On the flipside, though, it is not okay to turn perfectly good, locally-running software into a service just to extract a few more dollars from your customers. In the long run, this will drive users away from your platform — nobody wants their data or their ability to use a program they have come to depend on to suddenly be held hostage by its maker, who then demands monthly ransom payments. Eventually, there comes a tipping point, and customers depart en masse for something less invasive.
Don't be the reason anyone has to do that.