I prefer to cut my own yardage, personally speaking I wouldn't buy pre-cuts, my personal opinion.

I like the variety you get.
Block magazine is a great go to for using precuts.

I get them all. I have made quilt tops using charms and jelly rolls and had no problems. I have two layer cakes that I am waiting for inspiration for. I have thought of cutting the squares into 4 triangles and putting them back together scrappy.

I started using pre cuts some time ago. I prefer pre cuts now rather then yardage. I usually by layer cakes and charm squares. Theses shapes fit perfectly on my Go dies. I can get every fabric in one design in one pre cut pacakge. I use to buy fat quarter bundles but now I buy a layer cake. I really like the Dessert Rolls too. I have much less waste to fill up my scrap tub that is overflowing as it is. I buy yardage for backings, borders, and cutting bigger squares. Nothing inspires or motivates me more then seeing luscious pre cut packages filling baskets in my sewing room and they are so pretty. That to me is worth the price.

I have only purchased a couple of charm packs for quick table runner ideas and two jelly rolls, both with a specific project in mind. I own a few books designed for jelly rolls and charms but haven found much joy in choosing and cutting my own fabric...

I really like using jelly rolls for quilt projects, and many of the classes I enjoy call specifically for one or two of them. I have found, though, that I really have to be watchful since different jelly rolls are slightly different from other ones: recently I bought one that was actually closer to 2 3/4" wide. Every strip I used had to be trimmed down to 2 1/2" before I could sew it into a strip set. The other one in the project was exactly 2 1/2" to begin with. Since I am hooked on batiks, jelly rolls seem to give me more variety than any other precut. This seems to boil down to what I hear from so many other quilters -- do what makes you happy.

I have never used any pre-cuts. I'm probably the exception as many do use them. I can see the advantage of getting a variety of fabrics with them. I just enjoy the whole process of quilting so cutting my own doesn't seem like a chore and many of the things that I make don't use standard sizes that come in pre-cuts. Over time I have accumulated a stash and I never throw any scraps away so if I need a color here or there I generally have it. Whether you use pre-cuts or not really depends on so many things. One way is not any better than the other.

I do a lot of charity quilting, so precuts are my friend. I get a lot of variety in colors and designs that I would not ordinarily buy. I used to buy charm squares, but never seemed to have enough for the project in mind, so now I buy a layer cake and cut it into charms...voila 4 charms sets a couple $$$ cheaper than just buying the charm squares. I love Green Fairy Quilting.com for precuts, no shipping costs, and quick delivery. They have some great specials, and always the newest collections. I love getting batik jelly rolls, so much fun to just touch and admire all the color choices.

Whatever you buy, check to make sure there are many different fabrics. I love all of these, but I don't like it when I buy a charm pack of 40 fabrics to find out that there are only 15 or 20 different fabrics. I bought a beautiful jelly roll once from a vendor at a quilt show only to find out that she stuffed it with some ugly fabric and I actually had only 28 different fabrics. I love to buy from Missouri Star but I check out how many different fabrics are in each.

Like everyone says I think it depends on what you are going to make. I purchased a layer cake because the fabrics were very appealing to me but completely different from anything I had made before. So the layer cake gave me a sample selection of all of the different fabrics without my having to search. Also I had nothing in my stash that would "fit" with these fabrics. Just finished the quilt and I love it. But don't think I would do one like that again. Once is enough.
Also have to admit it did take me a while to find a pattern that used the layer cake.