I'm thinking the damp BB placed in a powder could potentially cause bacteria in the powder product. Especially a pressed powder. With a BB I have to get it wet, squeeze to get it to absorb the water, squeeze it out, then squeeze a little more in a towel according to the directions all before it's ready to use. I don't re-wet it as I go either, but as someone who's looking to save time those prepping steps are steps I can do without. With a brush I just pick it up and go to it. As far as cleaning, I feel like with the BB there is a lot of kneading going on to try to get the makeup out. Plus I have to be careful not to tear the sponge trying to get the makeup out of it. Especially on the tip. Could be the shampoo I am using with it. I don't have the BB cleaner, but was just thinking about it last night since I cleaned a brush at work with it. When I see the stains in the BB I'm never really sure if it's clean. Putting the shampoo in my palm and then swirling my UD brush firmly in the soap is much faster and less of a hassle for me. And again, for me, buffing is much faster and takes less effort than stippling for application. Stippling doesn't necessarily blend, however, buffing applies and blends at the same time.
I know people love the BB, but for me it adds too much time and effort. In the time it takes me to prep my BB I could have my foundation beautifully blended with the UD brush.