What are the deciding factors for a scan desgin

If u ask to do DFT implementation on a design, then what factors do we need consider mainly. While doing the DFT implementation designer need to have some knowledge on tester which will be used for testing IC.

• Number of channels available on the tester
• Memory size of the channel
• Number of scan pins
• The operational frquecny of the tester

This above facotrs must be considered while implementing the DFT on the design