Well, one issue is that any employee with customer contact generally has to be available for business hours. I can't imagine a sales or support issue being deal

Well, one issue is that any employee with customer contact generally has to be available for business hours. I can't imagine a sales or support issue being dealt with in the manner of "Sorry, you'll need to contact us between 10 and 2, except on Thursdays". Especially when you have 'clients' rather than 'customers' (~= people who generally expect some continuity in their contact points). You could argue for support to just 'simply' double the staff to cover the 8-hour day, but that has no handover time, and you also double the fixed per-employee training costs (both starting and ongoing training) and fixed HR/management costs.