The CPL includes 10 hours of IF, which can count towards the 15 hours required for an IR(R). So it only takes another 5 hours of IF to complete the course. If you have ATPL Theory you don't need to sit the written test. Hey presto, you have an IR(R) which is much cheaper to maintain than an IR, and gives you an extra ticket for not much effort. It also gives you a head start when training for the IR. I felt it was worth it to me.