As a subcontractor, main contractors often tell me about the benefits of partnering.
Maybe I'm just very suspicious, but I do wonder who is usually the main beneficiary from this.

My firm will often help out a main contractor when it is negotiating with its client – we regularly propose specifications and alternatives and advise on costs and quantities.

My idea of partnering would be that once the main contractor has finalised and agreed its bid, it negotiates with the subcontractor that assisted it, with the intention of using specifications based on its proposals.

Unfortunately, in the real world of subcontracting, it very rarely works out like that. The reality is that the main contractor will go out and get the cheapest prices possible based on its specifications advice. It will then run with the cheapest quote or use it to beat you down. That's fine from the main contractor's point of view, as the QS or buyer is only looking to improve its margins. But sadly, it does not encourage the subcontractor to spend a lot of time developing specifications and options. There is only one "partner" who benefits.