[jrumbut]

You either end up reinventing foreign keys, your support volume will scale faster than your data, or user experience will suffer.

There may be situations where foreign keys become too much overhead, but it's worth fighting to keep them as long as possible. Data integrity only becomes more important at scale. Every orphaned record is a support ticket, lost sale, etc.

[butlerm]

Orphaned detail records are usually inconsequential, like uncollected garbage. References to anything with an optional relationship should use outer joins as a matter of course. If you delete something that really needs to be there you have a problem, which is one of the reasons not to delete rows like that, ever, but rather to mark them as inactive or deleted instead.