For the most part, I like making the patchwork type quilts - so I did buy the 1.5 inch & 2.5 inch strips, the 2.5 inch square that will cut 12 at once. (yes you can take the strip die and reposition the fabric strips to make the smaller squares - but wanted this one and it was on sale.) And I bought both sizes of the tumblers, and hexagons were a must. And I got the triangles that go with the hexi's -- again because there was a sale. And then there are the 5 inch double square and the list goes on. I did buy one with circles - had this wild hair that I wanted to make a quilt with yo-yos, so bought the die and those little Clover plastic things that help you make them.
When they have a sale I check to see what is new and what I may need. I did buy the Double Wedding Ring because that quilt is on my bucket list and again it was on a very good sale.
I don't wait until I need it, because then I either can't find it, or it is not on sale. And I know what kind of quilts that I like to make. Also, Accuquilt has you accumulate points for each item you buy, then you can use the points for an additional discount. Even when they have a sale and you buy over a specific amount you don't pay shipping.
So the best thing to do is sit down, look at the dies available and decide which ones fit your style. Make a list and buy them as you can afford or need them. No reason to hurry. They do retire dies from time to time - but that is rare and they give you plenty of warning.
Enjoy your cutter!