What is the incremental benefit of AC canned outdoor coil cleaner?
I use concentrated liquid and will consider it the same as canned cleaner. 

Condenser cleaner or coil cleaner is formulated to take grease and oil out on top of the dirt. I use Nu-Calgon , Nu-Brite this is a non acid cleaner that mixed with water cuts the grease and oil and actually removes dirt better because of its foaming action. 

In my early days I used to use a surfactant this breaks the water surface tension and cleans the dust out better but you have to mix the surfactant and water (I use a 2 gallon pump sprayer) 

Over the years I noticed that some brands coils really collected dust compared to other brands, it turns out it is oil left over from the manufacturing process. Cleaning with a non acid cleaner will provide superior results (even simple green is better than water) I found the Nu-Brite and it works better , 

I proved the cleaners worked better by flushing with simple green, rinsing well then spraying with Nu-Brite as the foam pushed out the remaining dust I was quite surprised how much was left. A quick rinse and for grins I repeated , the foam was coming out clean. This is why I switched to “canned cleaner”  I also noticed after treating with the Nu-brite the coils were not as dirty the next time. I know part of this was cutting the oil and believe simple green did that but it did not push all the debris and residue out like the foaming cleaner.

This provides several reasons that cleaner is better than water, cutting oils, breaking surface tension and a foaming action.