I'd agree with Sue that it depends on the pattern. While patterns are becoming more standardized, there are still lots of patterns that use different ways of using measurements. (I personally think the ones that are most useful are the ones that give you a measurement of the actual finished garment. The most useless one I see given is where the pic is captioned "model is wearing a 34" chest finished measurement garment" or something like that -- without giving you the measurement of the model, so how is that supposed to help!?)
Also, as Sue says above, ease in knitted garments is very strange stuff. In many knitted garments, as you may already know, you actually want negative ease, and you will often find that the actual measurement of the finished garment is actually smaller than the measurement of the size it's intended for. Sometimes the measurement of a garment is smaller when it's lying flat than when it's hanging on a hanger or body, depending upon the weight of the fibers and the density of the fabric. And the amount of ease that each knitter likes is a matter of personal taste. Add to that, the ease given for a pattern often has a great deal to do with the yarn used by the designer...so if you're working in a different yarn, you might more or less ease than given.
Which is why I like patterns that give a finished size measurement, rather than saying "fits a 34" chest" or some such.