When two projects need the same resources at the same time, a resource conflict arises. Sometimes it can be the case of two projects wanting to have access to a specific individual, and in other cases there is a shortage of a certain competence. Project A may need 3 mechanical designers at the same time as project B needs 2 in an organization where there is only 3 of them. The simplest and the most common solution is to share that resource, i.e. to let each project have access to the resource half of the time. If a third project should then need the same resource, this can also be provided by letting each project have access to one third of the capacity of the resource.
The advantage of sharing resources is that it is appears just and that no one is completely dissatisfied. It is interesting to note that a version of this occurs in agile organizations. There, it is not the resources themselves that are shared since they are usually designated to a specific team and since that team has clear work tasks that are started and completed. Instead, the sharing of capacity between projects is handled by means of prioritization or pulling backlog items in such a way as to create progress in several projects. If project A is allowed to include two of their features in the next sprint, then it is only fair that project B should also get to include one or two of their features.
Are there any disadvantages with these apparently just and elegant solutions to conflicts between projects? Yes, unfortunately, there are some major disadvantages.