If it's hot & humid outside, I may forgo the water pan. Otherwise for brisket, ribs, pork butts, etc. where I want a deeper smoke penetration, I am a firm believer in adding some kind of water pan to the grill.
Sometimes it's a pan underneath. More often than not it's just some kind of pan or can off the the side.
Cheap bread pans work really well and can fit off to the side.
Even a tin can or two will work, and may be my favorite. They cost nothing and fit almost anywhere.
I also add hot water (not cool) to get it going as quickly as possible.
Here in Ohio, during cold weather the air gets extremely dry and that's when I notice the biggest difference in when I use a water pan. In summer time I don't really notice a difference.
"Why is moisture so important? Is the moisture creating nitrites, or simply grabbing the much more prevalent carbon monoxide molecules which also block myoglobin from turning gray? Water does a great job physically trapping smoke- a mechanical, not a chemical, process- but is that the whole story? What limits the thickness of the ring?
You'll have to wait until the next article is posted.
For now, the keys to producing a strong smoke ring are based on retaining a moist surface, through a combination of:
High humidity to reduce natural moisture evaporation, e.g. smoking above a properly designed water pan
Low temperature cooking, again to reduce surface drying
Avoiding strong air currents which parch the surface
Frequent wet mopping to maintain a moist surface- one of the few reasons to mop. A mop containing an acidic liquid (e.g. tomato, vinegar, mustard) and sugar stays moist between applications. If the surface ever forms a hard crust, subsequent mopping is less effective. Spraying with pure apple juice, onto a standard dry rub, tends to dry out between applications, but will somewhat increase the smoke ring."
This is for smoke ring but addresses the benefits of some kind of moisture being added to a low and slow cook. My ribs I like water pan my big meats I like spritzing. Just my take...