The advantage is when a new person starts. "How does this work?", oh here is a link to a well explained document on this thing called "Rails". Oh you know "Rails" already, of course you do, that's why we hired you.

Where as with a customized "elegant" meta-programming DRY NIH solution unique to ThisCorp. "How does this work?". "Try to figure it out yourself. Jack has left and Ryan is too busy fixing production issues to help you".

Obviously if you have a team of Haskell compiler writing geniuses YMMV.