A lot of people prefer it as its reusable, i.e you're just washing the fleeces and disposing of newspapers, as opposed to the cost of buying shaving or megazorb etc. For a lot of people with extra spacious cages this is cheaper than continually refilling their cage with a bedding type like this.A lot of piggies prefer it as it is comfy and soft and warm. Some people think shaving can irritate breathing, I never used to find this but may depend on the quality of shavings you buy.
It's personal preference really, and what works well for your lifestyle too.
I agree totally - disposable or washable depends a lot on your lifestyle and what works for you and you won't really know unless you try both but if you are happy with one, there isn't necessarily any reason why you should try another.
I have one set up with fleece (a c&c set up) and 3 set ups (double storey hutch and two shop bought cages) with Aubiose (hemp based bedding) which is disposable at present.
Traditional wood shavings can dry out guinea pigs feet a bit - you might not notice it at first but you will probably notice the (positive) difference a couple of weeks after changing from that to a different sort of bedding. I certainly did with ours. I wasn't having any particular problem with their feet either but I do feel now I won't go back to wood shavings ever having seen the difference.
I've used all of these at some point:
Woodshavings with newspaper underneath
Carefresh with newspaper underneath
Fleece with puppy pads underneath
Fleece with towels underneath*
Fitch with newspaper underneath
Fitch with nothing underneath
Aubiose with nothing underneath
Aubiose with an old shower curtain underneath*.
*=the 2 options I'm currently using
Happy to share my views if any of these appeal to you and you want to know more! But they are just my views. It's great that you care about your piggies but please do enjoy them and don't stress yourself out over the care of them. There are few hard and fast rules so you shouldn't generally feel or worry that you might be doing things wrong.