Personal preference and $, is what determines the lining, in my book.
I can and have done them both ways and prefer to use two leathers like KC to add up to around 10-12oz, when a customer wants a lining. I donot think that the purpose, or way that we use our guns now days has any resemblence to 1890. A holster then was simply a belt puch to carry a tool, with a minimal amount of asthetics. I don't recommend linings to my customers, but will make it however it is wanted. I donot use any chrome tanned leather or roughout pig or suedes. Veg tans with smooth sides out only!
I don't really think that the lining helps the ease of drawing, keeps the guns finish safer or cleaner, than unlined rigs and when I am building a holster there is an additional charge for lining! In the game we are in today, we buy a rig for several hundreds of dollars and then in a year or two sell or trade it. Not something I would want to sink a ton of money into. Kind of like buying extras or accessories for the company car we are going to trade in at a certain date or milage .......possibly but not likely. I just don't prefer linings.