This video is being discussed

[Apple Roof Cleaning]

The roofs came out cleaner with no runoff issues. We only had to downstream chemical on the roof and clean, so no ground guy was needed. Most ask for soft wash now, but I still get some customers that prefer this old but safe method.

I agree, sometimes there is a place for it. There are some tile roofs w/o guttters you learn to walk away from when chemical cleaning.
Over the years, you just develop a Gut Feeling about a job.
Certain Plants just can't take much or any chemical exposure. If you have a really filthy tile roof, sometimes it takes a little stronger chemical concentration to get it clean. The stronger a cleaning solution is, the faster it cleans, and the faster it kills plants too.
Like Nick says, some customers have ZERO Tolerance to even a yellow spot, here and there!

Sometimes, I sell tile roof cleaning jobs like this "Mr Customer, I can clean your tile roof 2 ways. If I pressure wash it, you may have cracked tiles, and it will not stay clean as long. Or, I can clean it chemically. The Chemical Cleaning is much safer for your roof, and will last longer. But, because of all these plants, and you having no gutters, there is a chance of a yellow spot, here and there."

This allows me to feel my customers out. Of course, 90 percent choose the chemical cleaning, but I have heard this before!
"My Wife will kill me if we yellow even ONE of her Plants"

I hate when that happens, but when it does we walk away (We do not own pressure washers), and we refer it out.