I was a clueless internal-routed newbie when I had to replace the RD shifter cable on my Specialized Roubaix last year and I can tell you that it was a major pain in the ass to thread. It wasted several hours. Next time I will tie a thread to the old cable so I can chase the replacement in and it may be easier.

So I am not a huge fan. Yes it looks cleaner, but it can be a hassle.