Well, I'm not representing myself as any kind of expert, but I have been doing this from the very beginning and haven't seen any big problems. Almost all of my phals are planted two of the same kind to a pot without any trouble so far, and I get big lush displays when they bloom. One problem is that they are a little harder to water properly because there are more leaves, etc., in the way--but no biggie.
Here's a pic of some paphs I have done this way; they have been blooming and putting on new growths like crazy. I call this picture "the confrontation" LOL