The Purchase Status field represents the stage of your transaction.
Every Closing will be created with Purchase Status = New File and from there you can change it accordingly with the progress made.
The most important options from here which are related to automations are:
Closed -> Date Purchase Closed field will autocomplete with the Current Date and in the Seller Leads app, the Stage field will change it's value into Closed.
Canceled -> Date of Cancelation field will autocomplete with the Current Date and in the Seller Leads app, the Stage field will change it's value into Dead.