Turning on the MIP strategy allows you to assign a crown to a limited number of projects to make them your "most important projects".
How to assign crowns to projects
To assign a crown to a project, click on the edit icon to the right (cog) and select the crown at the bottom right.
How to add a limit to the number of MIPs
In the strategy settings you can set the max number of MIPs you can have at any one time. If you want to assign a new crown when you already have 3 MIPs and your limit is 3, you need to first complete a MIP or take away a crown from one of the MIPs to be able to assign the crown to another project.
The limit can be adjusted anytime.
How you can tell a project is a MIP
A MIP will have a crown on top of the regular flag icon.