The program can be easily reused by adding a new smart campaign in the same program.
The "Program" contains both the Email message as well as any campaigns used to send that message.
The "Email" is the message you're sending
The "Smart Campaigns" are used to send the Email to various lists.
On Monday you create a Smart Campagn (say you call it "Send Group 1")
On Tuesday, you can simply create a second Smart Campaign with a new audience and call it "Send Group 2".
On Wednesday, you can create a third Smart Campaign and call it "Send Group 3".
If you want to make sure that nobody gets the same message twice, include the filter "Not Was Sent Email" for the email you're trying to send.