Chains wear faster when particles (worn off alu, sand) are present between the link parts' contact surfaces.
Oil makes them stick and oil does not dissolve in water.
Soap attaches to oil and makes it dissolve in water, and with oil removed, those particles are freed/don't clump, become mobile and can thus be washed away.
When to use soap depends on the amount of dirt. Oil reduces friction and thus wear, but at the cost of an accumulating particles quantity.

Water, oxidizes steel, rust. Rust occupies more space than steel, and also its poreous, it exposes even more steel, and dries harder, increasing the amount steel that gets oxidized. Salt is worser. Oil forms a film that protects steel from rust.

Thus, tbe goals are keeping a chain dry, hold off foreign particles, and get worn off steel and aluminium (chainring) particles out of the links.

My "regime" is to put a drop oil on the rollers of the chain, from the inside (centrifugal force see later) so on the lower part of the chain, and only in oxidizing situations (rain, salt) with a tooth brush some oil on the sidewards surfaces of the link plates and especially the pin ends.

The next days after riding I see then black (particles) oil spilling out to the outwards edge surfaces of the links, brought there by centrifugal force. I wipe that off, and that is byebye particles.
Then, when the chain becomes too dry from oil (reason the described mechanical degrease), I repeat.

Notes:
- alot oil makes a first fast ride and a next slow ride, due to the ton of dirt on it.
- don't put water on a chain that has salt on it (ex road salt in snow that sticks on it). Salt dissolves in water, becomes as mobile as water, and will then reach the contact surfaces in the links, and cause massive damage in a short time. Salt does not dissolve in oil, so a protecting oil film on the outer surfaces of the links and wiping it off later on will rescue the chain from the garbage bin.
- prevent water condensation on cold surfaces (metal). Stalling a bike in a place with nightly temperature drops will condens water in air (humidity) on the steel, causing oxidation, especially on the places that gravity brings the condensed water to. For ex if you stall the bike against a wall, so tilted, the water will end up on the pin ends, about the weakest points of the chain, ex fretting away the metal of a rivet causing the link plate to detach.
- riding a bike dries the chain just like wind dries up water. And the pedaling force pulls the links abit away from eachother, allowing water and dirt to escape easier due to more room available.
- compressed air blows away the most liquid (water) to leave the dirt immobilized behind, and usually even closer to the deepest places in the chain: the contact surfaces. Selectively wiping it off is slower but better.

/end of blahblah