A subproject has almost every time the same client than main related project. At now, we have each time to retrieve it in a list of 300 (at now, but growing) clients!
So it would be useful to have the 'client' field set by default to the same client than parent.
Only default, not forced (just pre-positioned, with scrolling list still present), because it may be different in some cases (p.e. when main client is a subcontractant wtih subproject for one of its clients – and we have final client-specific data to use for the job).
Similarly, the list of facturation contacts should be restricted to the selected client’s contacts and not having to retrieve the good one in a list of more than half-thousand!
That would contribute to avoid some input mistakes.

And that principle could be applied on some other input screens.