Your team does not need to wait for another Scratch Org to spin up if they can take one from the pool. Here is how it works:
Under "Scratch Orgs," click on the "Pool" tab
Click "Create your pool"
Control the pool size with the "+" and "-" buttons
Find further settings for pool orgs under "Project Settings"
If you change your configuration, or you merge important changes to your main branch that are required in all environments, you can easily refresh the pool with a click of a button
Sometimes, when creating a brand-new Org – whenever one is taken – it can matter to pick an Org from a specific creation time (often the most recent one). Our pool has a "Take" action in the context menu of Pool Orgs.