Every person has a different ability to recover, and has different goals.
After 35 years in the weight room, I rarely get sore. My body is very adapted to high loads and I also have the good fortune of good genes, and I stuff myself. I'm also a classic mesomorph, having weighed 140 as a freshman in high school and 175 as a senior in high school at 5'5" with the fifth highest strength index in my school. I've been tested by various organizations over the years for my abilities.
When I was younger, I trained every body part twice a week. I was hard, and dense, and strong, but, not really big and full. Now, I train like so: back and bis, chest and tris, quads, shoulders, hamstrings, arms, rest, repeat. I've found that the extra recovery has allowed me to maintain my weight better, and to be bigger and stronger. Bodybuilding is about cosmetics / appearance / fitness. Weightlifting is about power and the ability to move a weight through space. The two are not at all alike. Size is more of a function of endurance (read up on sacriplasmic hypertrophy), where strength is the ability to generate short bursts of power. Bodybuilding requires more power output over a longer period of time, and, for cosmetic purposes, generally, requires that you maintain a much HIGHER fitness level to stay lean, and that you maintain enough calories to maintain a high activity level to maintain a high level of fitness.
More than any single thing, CALORIES are the key to gains. You GROW on your days off, AFTER the training stimulus.
What works best for me, or another guy, may not work for you. If you don't eat enough, you're better off to only train parts once a week. If you haven't trained long that's probably a good idea, too. However, if you eat like a pig, and have been training for years, are an accomplished athlete, and are a classic meso, you can train much harder without over training.
What it gets down to is your ability to judge your ability to recover. You have to apply good science to your situation and learn everything about the human machine and how it works. There are many different models of the human machine. One version of training does NOT fit all. If you aren't gaining, though, you ARE NOT EATING ENOUGH.
Many folks do horrible form, lifting WAY TO HEAVY, in to low of a rep range, and not consuming enough calories. Sport is science, genes, natural ability, experience, and technique, whether it's how you play hockey, row a boat, ride a sled, or tune the human machine to a higher standard of performance.
Lift in proper form, through a full range of motion, and stretch at the end of the exercise.
I.e., eat; don't train like an idiot; do what works best for you.