An unexpected tool makes it easier and more economical to apply conditioning to leather boots and shoes, which leaves them waterproof, comfortable and long-lasting. There are thin, watery products available for waterproofing boots, but I find them not nearly as effective as the thick brush-on variety. Instructions for those say brush on the material, let it sit, then wipe off the excess. Not all that much is absorbed into the leather, though, and what you wipe off does the boots no good and is just wasted. If you do not remove the excess, it can collect dirt. The photo shows the brush-on conditioner applied to just the toe of one boot, unheated. I use "Red Wing" brand, just because it was available at the store where I bought the Red Wing boots.
To see my related Instructables, including how to apply no-slip spikes to the bottom of work boots, click on "unclesam" just below the title above or in the INFO box to the right. On the new page that appears, repeatedly click "NEXT" to see all of them.
Unclesam

Step 1: Gun Those Gunboats

The near boot has been slathered all over, and the toe is being warmed using an electric heat gun, its shiny metal tip visible at the right edge of the photo. The conditioner begins to glisten as it thins, and as the leather cools, it sucks all the conditioner into it, none is wasted. I use my Wagner Paint Stripper gun, which has a variable temperature control. The gun is set to about as warm as my bare skin can tolerate, and it is constantly kept in motion to keep from damaging the leather. I have never tried another kind of heat gun, hair drier, etc., but they might work just as well.

Step 2: One Boot Finished, One to Go

This trick worked so well that at first I worried that the heat gun might just be evaporating the conditioner. I played the heat gun on conditioner that had gotten on the manmade parts of the shoe, which do not absorb it, for a long time, and that material never disappeared. Clearly, the heat was just causing all the conditioner to be absorbed by the leather, not evaporating it. Excess conditioner that gets on the manmade components needs to be wiped off or it will collect dirt. Applying the conditioner heavily particularly to the stitched seams helps keep the boots waterproof.
The heat gun also causes regular shoe polish to be absorbed into the leather of dress shoes, rather than have it be wiped off by buffing.
I always wear heavy boots when I do outdoor work around my yard, sometimes in wet areas. For decades I bought department store boots, on sale, replaced them when they wore out. In my dotage, I realized that my feet had suffered, so I bought these really sturdy, comfy Red Wings, which were expensive. To protect my investment I have regularly applied the conditioner, and these boots have provided many years of service under tough conditions. Same applies to other brands, but if you want to find Red Wings, look in phone book yellow pages or do Internet search, as they are usually sold in freestanding independent stores rather than department stores or malls.
U.S.
CREDIT: Photo background made of genuine pegboard.