I had long ago abandoned using shave oil as part of my double-edge-razor-shave prep; I found it messy and unnecessary. However, using the straight razor has opened my eyes to subtle benefits of using a shave oil underneath my water-based shave soap.
My Process of Using Shave OilBefore I go on, I should explain the process I prefer when using shave oil. First I ensure my beard is well wetted with warm water. This can be done by a pre-shave shower, or, because I tend to shower in the evening and shave in the morning, I do it this way: I rub warm water into my beard several times. Then I take a washcloth wetted with very warm water and hold that against my beard for about 30 seconds.
After my beard is warmed and well wetted, only then do I rub in shave oil, which can be as simple as any inexpensive kitchen oil or a scented, dedicated shave oil.
After that I rub dry shave soap on my wet, oiled beard, and use a warm, wet brush to face lather. (Because a proper shave soap is not formulated with fatty acids that aggressively remove oil, this isn't a counter-productive process. However, if one were to use face or hand soap as a shave lubricant, then the soap would tend to remove the oil from the skin.)
After my shaves, I've been using the same wet cloth, but now saturated with cold tap water, and holding that against my shaved skin to sooth and calm.
The Lingering Benefit of Shave OilI've been finding that following this process leaves just the slightest trace of oil on my skin, which seems to diminish any need for after-shave balms. I'm going to start using oil with my double-edge shaves as well and try that out for a while.
Using this process, the only reason I've had for post-shave liquids or gels is to apply any lingering fragrance that I may desire.