I think the origin was hydroponic growing. I saw higher concentrations of H2O2 at the hydroponic store, to be used diluted in the reservoir.

I use 3% first aid strength to clean off mold on the exterior of terra cotta pots.

I don't see it having much use for orchids. I did find 3% to have some utility in preventing the fungal disease known as "damping off", which causes plants to rot right at the soil line when growing Mesembs, a family of succulents very prone to the disease. I simply watered normally with the peroxide. However I found that germinating them outdoors in full sun was even more effective, probably due to a combination of air movement and UV exposure.

I did some peer reviewed literature searches awhile back and couldn’t find any information backing up peroxide use as an effective antifungal or soil oxygenator. I was able to find information on tissue damage, mostly related to why it is no longer used in wound care.

I have used it to treat crown rot in a few Phalaenopsis because it made sense to me that killing all the exposed rotting tissue could be a good thing. I also dried out the excess peroxide and packed the crown with cinnamon. I did save the three plants that I caught early. I wonder if it was more due to the desiccating action of the cinnamon?

I was once on the 'bandwagon' of hydrogen peroxide, which was based on reading about people's usage of it.

But I don't use it anymore - mainly because I ended up finding I already have methods (not involving H2O2) of treating relevant orchid issues (or pre-treating orchids) when needed, and secondly - it just 'seemed' that while application of 3% H2O2 didn't kill any of my orchids that came in the post --- it appeared (due to observations) that it affected the roots and/or plant in some way ----- as in it took a relatively long time - several months - of the plant doing nothing - suspended activity, before the roots and/or plant was able to get going again. It just appeared to me that H2O2 was holding something up --- with the plant, as if the roots or plant needed to recuperate from its effects.

Sometime - in the future- I will probably get around to doing a bunch more observations - comparison tests, as I haven't got any way to 'measure' what's going on at microscopic levels. Hopefully some sources or studies can be found to save us the time to look into this.

Also --- thirdly, I read that once a new bottle of H2O2 is opened ----- degradation of H2O2 begins to occur, creating another possible drawback.

I'm not opposed about the usage of some product, like H2O2 - as long as there's some good and proper evidence that supports it. I don't use it anymore though - not for the purpose of diluted sprays on orchids that is.