I find the most effective use of that claim is it's ability to sell pre-made compost teas. Unfortunately, those claims have occasionally become popular with the make-at-home compost tea crowds.

It's disease preventative measures are also highly overblown.

It's a nutrient and microbe source...especially a good nutrient source for micros when properly balanced...and rather wasteful when it is used as a foliar feed.

Fwiw, compost tea used as anything other than a nutrient and microbe source has had it's strongest consistent benefits on fungal diseases. Some of this might have something to do with the pH of the applied tea, though...the mode of interaction is unclear. It still doesn't make for an extremely effective fungicide for many people, though some studies have found less fungal issues using compost teas (especially on turfgrass).

It's also worth mentioning that a healthy almost-anything is less prone to disease than an unhealthy plant suffering from a nutrient deficiency.

There are many claims for the benefits of compost teas. Most of them are anecdotal, advanced by the practitioners and sellers of compost tea. Few of them stand up to controlled research. The one possible exception, as nc-crn noted, is disease suppression where anaerobic compost teas does seem to have some benefit, which has not been as clear with the more common aerobic compost teas. The presentation linked below might provide some helpful insight.

Here is a link that might be useful: U Ky Compost Tea

Thanks for the insightful replies! I figure its mostly anecdotal info, though enough people seem to brew or steep their own that it seems it might be worth it to try out, especially as a microbe source. Do you use it? Would you recommend giving it a try anyway?

I take it information on compost teas should be taken in the same light as mycorrhizal amendments? One of those YMMV things.

I use it every couple of years (along with kelp/seaweed and chicken manure in the mixture with the compost) in a tea for microbe + micronutrient help (as well as a natural fertilizer bump of N/P/K - Ca/S).

I apply it in a soil drench directly to the soil a week-ish before planting or mid-season on my summer plantings depending on how lazy I've been (aka, usually mid-season).

I avoid using it on seedlings because of how much I use and the chicken manure content bringing possible "burn" to small seedlings. I'm not a fan of using it sparingly many times a year. I like to make a batch and use it while the microbes are alive/active and put it in the soil where they can thrive...plus I don't like making it very much so I do it once-and-done.

I don't use it. I prefer to apply compost directly to the soil. I personally see no benefit of brewing a tea over just using the compost.

I like iced tea over compost tea.

I make tea with vermicompost. When I make it, I use fish tank bubblers and add unsulphured black strap molasses to stimulate good microbial environments. I drench the soil of my new beds with it and water/fertilize the established beds by drenching their soil with it, occasionally.

I just did so on my Kale two weeks ago. This kale is in its third season. Leaves grew amazing after. Now it's cool. Time to harvest!

if I am regenerating existing plants (fertilizing) I add powdered alfalfa for nitrogen, too. Sometimes, I will add powdered egg shell. As I learn more about my soil and missing nutrients I will be able to add different ingredients to enrich the soil.

The goal of any form of compost - whether liquid or solid - is to make nutrients available to the plant in such a way that gives it strength to fend of pests and diseases. Even weak solid composts are good by providing the right pH balance and aerating the soil.

Some say foliar feeds are helpful. I have yet to see results of foliar feed being any greater than soil drenches. The longer a liquid "tea" is out from under aerated brewing, the less its quality. I believe time spent in a bottle produces much weaker tea, over time.

I'm still learning, though. I think foliar feeds is a good way to conserve the amount of tea if you don't have a lot of compost.