Treated leather is far more waterproof and resistant to wear and rot. During the rainy season I have seen new boots left untreated fail at the junction of sole to upper because of rot in two months.

Kiwi wax is okay for smooth leather. For a time I used Snow Seal. It is okay for smooth leather and cold weather use. A hair drier to warm the leather and it melts right in. The down side is that soaked in the leather becomes pretty much impermeable. Waterproof but it doesn't breath much and it has to be reapplied regularly.

Then I moved south and the ability of the boot to breath became more important.

More recently I have shifted to silicone. I got a quart of the stuff and apply it with a foam brush. When boots are new I lay on a heavy coat and recoat every few weeks for a while. Don't put too much on all at once as it can weaken glues. It will also make blond rubber darker amber and a bit harder. Seems to make the rubber less adhesive but wear longer. An acceptable trade-off in my book. After a few times the leather becomes pretty much waterproof and won't rot. After that point I might add more once a year or so.