Quickload is one of those things that you don't know how you ever managed without it till you have used it for a while. It's amazing how slight variables can change a safe load to a dangerous load in a heartbeat. Case capacity comes to mind. I measure my bullets weight and length and my brass' case capacity and length, and enter these values instead of relying on the default info for a specific bullet/cartridge. You will acheive much more accurate results this way. I reload for 300 win mag and the difference in case capacity of the brass in that cartridge from brand to brand is FRIGHTENING! (from 88 grains H2o to 95.5!) So if you developed a hot load in the larger cases and jammed that same charge into the smaller one, you'd have a 13,000 psi difference according to QuickLoad! Needless to say, if you're anywhere near max, you'd have a very dangerous situation! I always measure my case capacity now when I get new brass and enter it in QuickLoad for safety/accuracy reasons. Another example would be a 308 win load vs 7.62x51mm NATO. With the NATO's thicker brass, loads can use up to 2 grains less powder to acheive the same pressure because of the smaller case capacity.
Another great thing about QL is barrel time. Using an OBT (optimal barrel time) table, you can find where the accuracy nodes are respective of barrel length with a given load! I came to this conclusion on my own working with QL. Then I came across all this! It's helped me get very close to some pretty accurate loads in both 300wm and 308 win!
https://www.google.com/search?q=using+quickload+to+find+obt&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari
Does take a little of the experimentation/shooting/fun out of it though!