All of the tools now allow users to use either a thickness factor or a dough batch/dough ball weight to determine the amounts of ingredients to use. Originally, the first tool, the so-called Lehmann dough calculating tool, could only be used with thickness factors. That tool evolved from work that Tom Lehmann and Dave Ostrander did with crust thicknesses. An example of a discussion of thickness factors and their use can be seen at http://www.pmq.com/mag/2004november_december/lehmann.php
In the course of developing the preferment dough calculating tool, a few members who were beta testing the tool asked if it was possible to work with dough weights, which they preferred to work with, rather than thickness factors. That was simple enough to do and that feature was incorporated into the preferment dough calculating tools and all the other tools as well, either from the outset or as upgrades.
In some cases, dough recipes specify just a dough batch weight and from which it is not possible to calculate a thickness factor. For example, the dough batch weight might be 50 pounds, to make a lot of pizzas, or it might be 16 ounces, to make a single pizza. To calculate a thickness factor, you need a dough ball weight and a corresponding pizza size. In other cases, the dough ball weight and corresponding pizza size is given, so the thickness factor can be calculated. Wherever possible, I try to calculate thickness factors since several members have been accustomed to using them. The dough weight approach is technically the more accurate approach. But, I, too, started out with the thickness factor approach and became familiar with the rough ranges for that measure. For example, "thin" under the Lehmann/Ostrander approach is 0.10-0.11 (although members often use a thickness factor as low as about 0.07). "Medium" is 0.11. "Thick" is 0.12-0.13. "Sicilian" might be 0.13-0.14 or higher. But these are only rough guidelines. Deep-dish doughs commonly use 0.11-0.13 or so. Cracker crust doughs commonly use around 0.05-0.06. A Neapolitan-style crust based on using 00 flours can range from about 0.065-0.13 depending on whether one intends to bake the pizzas in a very high temperature oven or in a standard home oven (the lower end of the range is for high-temperature ovens and the higher end of the range is for standard home ovens). The Raquel thickness factor is 0.07-0.08. I have found that I can sometimes spot and help solve problems from just knowing the thickness factors in relation to the styles and sizes of the pizzas to be made.
My advice is for users to use the approach with which they feel most comfortable. And feel free to experiment.