I use them for cutting around pattern pieces on a large mat. The mat costs more than the cutter.
It's faster and produces a cleaner, more accurate cut. I wouldn't do it any other way now.
Cheap "Jakar Rotary Cutter" from "The Range", cost only £2.99. I've used it 5 times on full patterns and many other times for cutting curtains etc. It's still sharp and 28mm replacement blades are cheap at 10 for £6 on eBay. The only down side to this particular cutter is that the blade tightening nut has a tendency to work loose, requiring periodic adjustment.
Rotary cutting is the way to go IMO. Just get a large A2 sized mat (or larger).