Luciano, let me see if I can explain it for you. I've been cooking for years on a medium-priced offset stick burner...an Old Country Wrangler, to be exact. So, I've worked with a lot of wood and ran into all the issues of using wood primarily to cook with. I have produced a lot of good meat on that smoker. But, I was always having to check temps, add wood, open vents, close vents, add more wood, etc. It would just work me to death. And, with a stick burner, yes...wood is your smoke producer and your heat producer. I only used one charcoal chimney of charcoal as a starter. After that, it was adding 12"-16" wood splits all day. So, I was constantly adding wood, as you said, to keep the smoker going.
However, most meats, after they reach an internal temp of 140*, will not take any more smoke. So, any smoke you put to the meat, after they reach 140*, is not doing anything.
Now, since this is a Weber forum, let's talk about the WSM. I just bought a new 22.5 WSM, and actually did my first two smokes on it this past weekend. I had no idea how much wood to use. But, I keep a 1/3 cord of post oak, a 1/3 cord of red oak, and a 1/3 cord of hickory to smoke with on the stick burner. And, I cut up several of my post oak splits to use for these first two cooks on my WSM. Hickory is a tad harsher than the oaks, while the oaks, especially red oak, tends to burn hotter. So, I wanted to start a new smoke with the wood that I use the most, and most familiar with...post oak. I put 4 fist-sized chunks of post oak on top of a layer of charcoal in my charcoal basket, and filled the basket up the rest of the way with charcoal. Then, I put 4 more fist-sized chunks on top of the charcoal. Then, I scooped out a little hole in the middle of the charcoal and poured about 1/3 chimney of burning charcoal in the hole. Of course, it smoked bad for about an hour. Then, I could see the thick white smoke finally dissipated, and the thin blue smoke (TBS) took its place...and this is what you want...TBS always. When people talk about an ashtray affect, or something like that, it's because they've been smoking their meat over thick white smoke...and you never want to do that. Anyway, I knew when I saw the TBS, it was time to put the meat on.
I used the same amount of post oak wood chunks on the 6-hour smoke as I did for the 12-hour smoke...8 both times, and could see no difference in smoky-taste. And, the amazing thing to me was my ribs and ham on the 6-hour cook, and my pork shoulder on the 12-hour cook, were all just as smoky with 8 chunks of post oak as they would've been using 10 or so splits for the 6 hour cook, or 20 or so splits for a 12-hour cook on my stick burner. My personal preference is to taste enough smoke to know it is barbecue, but not too much to over-power the meat, or to not allow you to taste your rub. And, I think I got lucky on my first smoke on the WSM and found the right amount of smoke for my taste. However, I believe I will cut that to 6 chunks, 3 on bottom and 3 on top, when I try hickory wood. Not sure how that will do, I'll just have to play with it and figure it out...may have to cut it to 4.
I will say I was worried on my 12-hour cook. I started it at 10:00pm, put the meat on at 11:00pm, and went to bed. When I awoke, 8 hours later, my grate temp was down to 200*, and the internal meat temp was in the stall at 160*. Being my first cook on a WSM, I really didn't know what to do. So, I opened my charcoal door, used my fireplace poker and stirred up what charcoal was left. Then, I added 4 double handfuls of unlit charcoal on top of it. I was afraid it was going to return the thick white smoke like it does on first startup, but it didn't. It just slowly started raising the temp, with no smoke. Within about 15 minutes, I was back to 250* grate temp, and finished up the pork shoulder in 4 more hours.
My new 22.5 WSM is the most amazing smoker I've ever used! I just wish I'd bought one years ago. Good luck!