Why? Not everyone has a super sucker with a #10 pump on it. Not everyone needs a super sucker with a #10 pump on it. I have a tm with a 33 blower. On most residential jobs it is dry (within reason to touch anyway) in 2 to 4 hours with no booster. There comes a time for most people who don't need a super sucker to run a long hose run, or possibly dual wand one or two big jobs per year. Rather than run out and buy a new tm just for one big annual job, you can drop a grand on a box that will: give more flow to decrease dry times further, enable you to do some light dual wanding with a single wand truck, do upholstery and carpet cc at the same time, give you enough of a "boost" in suck so you can stretch another 100 feet of hose for that big job.
If you have a monster blower that flows 800 cfm and you only run 50 to 100 feet of hose on all jobs, you won't need one. If you have a smaller truckmount and need an occasional boost for bigger jobs without dropping the cash for a big tm you don't NEED, then it is perfect. Odin has a well designed box that can benefit most cleaners. Is it a "must have"? No. Neither is an airpath (which many scoff at) but it sets you apart and even if it is not a huge difference, it does make an improvement in dry times. The booster may not turn a small tm into a 800 cfm impresser of guys with little man syndrome, but it will give you that extra edge when you need it.