The ability to have multiple contracted proposals grouped under a single project. This is mainly for project management so you can pull in tasks, ordering, change orders, etc. under a single project that has multiple accepted proposals. This way if you have a Prewire/Trim Proposal, Lighting Control Proposal, Motorized Shades Proposal, etc. all under the same client you can manage them from a single project without having to keep up with them all individually.