Fabrics cut on the bias either have "drag" or "lift". Fabrics such as crepe, jersey, or charmeuse are among the fabrics that can be said to "drag" or "drop" on the bias. Fabrics such as taffeta, chiffon, broadcloth, or organza "lift" on the bias. Either type can be used to create a beautiful garment, but drag is better suited to revealing the form underneath, and lift, to concealing it.
I don't think I could have put it better.
Now, here's where I always have a problem explaining the visual to clients, since both fabric types are "right", but achieve different effects. Garments constructed of bias-cut fabrics with "lift" can create that "I feel fat" result. No, it isn't slimming, but it doesn't hug, either. Really nice way to understand which effect you want BEFORE you begin.