I can't speak specifically to knit patterns, but patterns for clothing in general usually should have a balanced side seam -- that is, one that runs down the center of the side line of the pattern. The exception to this is seams that are pushed forward or backward for reasons of style and design; when you're working in fabric, though, you have to watch the grain line when you do this -- in knit, it's probably less of a problem, although on an unstable yarn, a seam can help support the weight of the garment.
Some designers will push the side seam forward, feeling that it's a slimming line -- try it and see of you agree. It tends to work better if it's a set in sleeve with a close-fit armscye, rather than a boxy, loose fit.
Anyway, all of that is to explain that the measurement of the front half of the ellipse of a person's body usually is bigger than the back, whether man or woman. Breasts and stomachs must be allowed for. In a knit, you can often get away with not changing the measurement of the front, due to the nature of knit fabric and how much ease is in the pattern. The tighter the fit, the more you need to allow for the front being bigger than the back in order to keep a side seam properly balanced and the grain on-line and the fabric undistorted.
Even with a knit, as the fit gets tighter, the more you stand a chance of distorting the fabric as it stretches to cover bigger bumps, so a lot depends on how much distortion of the fabric is acceptable to you.
There's been a discussion in the pattern forum on a pattern called Tatiana -- I haven't been following it, but when I glanced at it fairly early on, the picture seems to me to show that it's an example of a designer who was not allowing for the body not being flat.
ETA: You can usually tell if a sweater needs shaping by simply looking at the seam while it's on the body. If you're examining a plain old regular side seam, stand sideways to the mirror and lift your arm so you can see it. If it's pulling forward or backward instead of running a straight line down, you know that you should add width (or subtract it, in some cases) where it's pulling. If the sweater has enough ease that the seam is running straight, don't worry about it.