To maximise the full benefits, the building owner must own the BIM.
If an engineer, for example, creates a BIM and does not share it, then the true benefits are not realised. For example, the designs across the design team will not be fully coordinated, the construction team will not have the chance to model the construction process digitally (or have to re-key the information to do this) and the building owner will be left to manage the facility with boxes of paper documents.
To maximise the full benefits the design team must share their information model, pass this to the construction team and then place in the hands of the building owner.
A very simple analogy would be to compare BIM with commissioning a book or a photography session. If the client only received a physical book or prints at the end of the process then that would be satisfactory, but receiving the digital content for the book or the original digital photographs is far more valuable. The client can reuse this content in future and get much better value out of it.