After I had my sewing machine for a few years and I had dilly-dallied with making very very simple things like tablecloths and questionable seat cushions, I decided to take an in-person sewing class in my city. That instructor only had us use sewing scissors to cut our fabric. Sometimes that instructor was too prescriptive, so after that class I ended up building my sewing skills from online (free) tutorials. That is when I learned of the almighty rotary cutter. Everyone was using rotary cutters in these videos - EVERYONE. I was fascinated and decided to buy one for myself and try it out.
I bought a Fiskar in this beginner set (Fiskar's Garment Sewing Starter Set - I would link to Fiskar's directly, but for the life of me I cannot find this on their site) from my local sew shop which includes a rotary cutter, scissor and thread snips.
There is a time and place for sewing scissors, but the rotary cutter just makes life so much simpler. It's really easy to cut along curves, and you don't have to lift the fabric up to get the scissor blade underneath it to cut it. Moving fabric can accidentally misaligning a pattern or, if you're cutting multiple pieces of fabric, one of the fabric pieces. This was why my sewing instructor preferred shears.
Note that if you do purchase a rotary cutter, you'll also have to purchase a rotary cutting mat. It's a big rectangular plastic mat that you can use underneath the rotary cutter so you don't cut-up your table or whatever surface you're using. The mat I have is a Fiskar's 18x24. I'd suggest getting a bigger one if you have the space and the money, but this one works just as fine if you're just testing it out, have a small space or planning to travel.