Currently there is an insight (called "Fundraiser Prospect and Opportunities) which displays the number of prospects assigned to a fundraiser. This is a great insight but isn't useful in its current form in my opinion. 

The number of prospects assigned to each fundraiser includes assignments that have an end date entered i.e. not active anymore. This confuses our fundraisers due to the number not matching their Workcentre portfolio and inflates our portfolio numbers on dashboards.

Even if you have access to create custom insights you are presently unable to create an insight to display on a dashboard which reflects the same number of prospects in a portfolio in the same way that the Workcentre does. Would love if this can be fixed.