Meaning of total slack in a project scheduled from a finish date

[Michele]

Has anyone of you clear in his/her mind what is the definition of the total
slack of a task in a project scheduled from a finish date?
Thank you

 

[Rod Gill]

This is one of the problems of scheduling from a finish date. By default
everything starts as late as possible, so everything is critical. You have
to manually add lag etc to create slack. I find that by the end of a
project, scheduling from a finish date takes up to twice the effort to
maintain.

Much better to schedule from the earliest start date going forward and set a
deadline on the last task to finish.