A size chart gives all the body measurements that the sizes were drafted to fit, whereas a finished measurements chart give the actual garment measurements. These will be different numbers, and comparing the two charts will show you how much EASE the garment has.
Simply put, the amount of ease in a garment determines how tight or loose it fits.
For example, if a stretchy garment such as leggings has a hip measurement that is 2" smaller than the hip measurement on the size chart, that means there is 2" of NEGATIVE ease - and they will fit tightly.
If the body and garment measurements are the same, then the garment has ZERO EASE. Keep in mind, this will fit differently depending on the amount of stretch a fabric has. If it stretches easily, the garment will have a nice relaxed fit, skimming the body without feeling tight. BUT, if you are using a compressive fabric that has to be pulled hard to stretch, it will resist stretching as you move, and it will feel tight.
When the garment measurements are larger than the body measurements, this is POSITIVE ease. All clothing made from woven fabrics will have positive ease - the higher the number, the looser the fit. Even a fitted woven garment need a little bit of of positive ease, so you can move in it. A knit garment with a small amount of positive ease will feel much looser than a woven.
So, looking at the finished measurements will give you an idea of how much ease the garment has. But that's not all we can use them for!
For example, if the sleeve length listed is longer than your arm length (from tip of shoulder to wrist) then you will want to shorten the sleeve. Arm length is not often included in size charts, and sometimes a child's height size is different than their arm length size.
So as you can see, finished measurements can be very useful. We provide them in all Goober Pea Designs patterns, with both metric and imperial measurements.