When it's safer to go below and use all the runway than it is to waste the runway and land down a third of it.
When is it safe to go below...when you have obstacles in sight, and can, in your professional judgement, do so.
In the summer time, I shoot to land well short of the runway and my wheels touch the tarmac on the end...I don't waste any. I'd sure feel like an idiot needing runway and leaving it behind.
Other types of operations, I don't do that...but some, I do. Where it's necessary, and appropriate. The airplane isn't on rails; it's flexible, and can be made to do what one needs it to do. Safely, professionally, and legally.
The circumstance dictates, as always.