If your teams work Sat/Sun then their workweek isn't really M-F and the workweek calendar should be set accordingly if planning is your priority. In this case you can either enter workweek exceptions or global non-working time to handle unworked weekends.
Some customers chose to end the weekend task on Monday and keep the M-F calendar. Assignees can enter time against a task for any day regardless of the workweek calendar setting - so they can log time for Sat/Sun.
A good feature enhancement would be something like the opposite of a workweek exception - a workweek inclusion or global working time but I don't know that enough customers would need it. Lets hear from you via the Greenhouse or Product Feedback!