When to segment vs create a new list?

When to segment vs create a new list?

When using autoresponders in workflows, when would it be best to segment a list rather than to create a separate list and add or move a contact to the second list?

Some situations:

1.  I want one workflow and set of autoresponders for leads who did not open the welcome or second email versus leads who opened the welcome email.  Should there be two lists or just segment one list?

2.  I want a workflow for leads who opened the initial email so that I can provide general information follow-up emails (sales, deadlines, happy holidays, etc.), but I also want to encourage leads to identify particular interests in our various services and send them additional emails that focus on their particular interest.  Should I have multiple lists or simply segment the list?  (And explaining why would be very helpful.)

Thank you.