I always thought that back-to-back par-3 holes were a design taboo -- something I would never want to do. That was partly because any time you do it on a great course, you invite comparison with the 15th and 16th at Cypress Point -- and you will never build two holes anywhere near as good as that!
Then, at Pacific Dunes, I just sort of fell into having them. Mr. Keiser was not too keen on the idea, either, but it was either that, or waste 100+ yards of oceanfront real estate, and I convinced him that was ludicrous. [Glad I did.] However, I was convinced that was the only time I would ever build back-to-back 3's.
Flash forward to Rock Creek, five years later. The long par-3 13th was in place on some earlier routings, but when we finally worked out the sequence of holes at the start of the round, the routing was 19 holes -- and most of it was one long loop, so it was difficult to throw out a link in the chain. The only place we had a hole going out and a hole coming back parallel were two par-4's just before the 13th, so Eric Iverson suggested we combine them into a short par-3 down the hill. It took me a while to overcome my natural resistance, but it helped a lot that the two holes were about 100 yards different in length. I do wonder sometimes if this is one of the things that holds Rock Creek back in rankings.
I have realized over time that I actually like what having back-to-back par-3's does for the pacing of the course -- by putting two of the short holes together, you wind up with a big stretch of longer holes somewhere, which can get you into a good rhythm. Even so, I'd never do it again unless both the par-3's were outstanding ... and I couldn't figure out another solution that was nearly as good.