A maximum working week would benefit an economy overall. When you allow a person to only work so many hours every week, you are also giving some one else the opportunity to work the rest of the hours. This creates many more jobs in the economy, which fundamentally creates a better economy.
No, a maximum working week would not benefit the economy overall, because not all jobs are created for a certain number of hours. Some jobs might be very busy some weeks and not busy at all other weeks. Requiring employers to make a job fit neatly into certain hours increases costs for employers, who might have to hire two people to do what is really only one job.