Why you (probably) shouldn't buy the biggest loomloom buying guidegetting started
Some people are tempted when buying a loom to buy the biggest one they can find, so that they can weave anything. But my advice would be to find something large enough to keep you interested, but small enough to fit your life. There is truth to the idea that if you get a wider loom you can weave anything on it, however, that doesn't mean bigger is always better.
One big advantage of small rigid heddle looms is that they are extremely portable. It's easy to move them around the house to weave where you feel like it in the moment. For example, sometimes it's nice to take my loom outside, or sometimes I weave in front of the TV, or sometimes I weave at the dining room table. Little looms can also be great to take with you to a social craft night or on a road trip. The bigger the loom, the harder all these things are. That's not to say there's not a space for big looms, but if any of those are things you might consider doing, get a small loom to start! A small rigid heddle loom makes a great companion to a bigger loom of any type if you decide you'd like to explore the multi-shaft world in the future or get a larger rigid heddle.
The other downside to a larger loom is that bigger rigid heddle looms can be more awkward to weave on. The heddles are bigger, the shuttles that come with the loom are bigger, and it will be more effort to weave. This is doubly true if your project is much narrower than the loom - it will be harder to keep a 32" heddle straight when weaving a 10" scarf. If you want to weave both small things and large things, you'll likely be better off in the long run with 2 looms, and as a beginner, you're probably going to want to start with smaller projects. Rigid heddle looms make fantastic little looms but keep in mind that floor and table looms provide more support while weaving which makes them easier to use at larger sizes.
Smaller looms are also generally more flexible what position you weave in. Small, short looms (e.g. Ashford Sample-It, Kromski Presto, Schacht Cricket) can be used in your lap, while bigger looms will require a table of the right height or a stand. Around 24" many people start to find a stand much more comfortable.
So what makes a big loom? The smaller the better if you'd like your loom to be very portable, but in terms of weaving comfort, most people seem quite comfortable with looms up to 25" or so; but if you have short arms or shoulder issues you may want to keep it smaller. And while many people do start with a loom up to 32", there are a lot of comments about those looms feeling quite big. Ashford's 48" model seems to be quite a niche product and almost certainly shouldn't be the place to start your weaving journey.
I've started with a 16" Ashford Sample-It, which makes for a nice inexpensive lightweight portable loom. Some day I'll want a larger loom but I'm quite happy with this little one to start!