Although I am not currently preparing for a bodybuilding competition I still devote time each week towards practicing my posing.
There are a few advantages that posing practice has to offer:
1) Better control over your muscles which will have carry over to your form in the gym.
2) Increased cardiovascular capacity from holding your poses for long periods of time. Anyone who has devoted some time towards posing will know how fast you can become out of breath.
3) Learning to better showcase the results from your hard work for your progress pics. Both you and your coach will appreciate this. :-)
So make sure to devote some time each week towards practicing some poses and mastering control over the muscles you work so hard to develop.