I think you'll figure it out by dropping the "supposed to do" part of your thinking and experimenting. There's more than one way to do things, as you've figured out, and both lead to valid results with varying characteristics.
That said, time spent controlling the lighting will help you have better tones than dodging and burning. Under-exposed and over-exposed areas (depending on the film, dev, paper, etc) tend to have compressed tones that will not look as "natural" when adjusted by D&B than properly exposed areas.
On the other hand, if you like the look of D&B areas, then by all means go for them.
Anyway, most photos can use some D&B to adjust more finely the tones.