I've griped before on these forums how fast-food places make their employees sound mentally challenged by forcing them to multitask in the drive-thru...taking orders, assembling orders, and taking money at the same time. The conversation goes like this:
"May I help you?"
"I'll take a hamburger and fries, please."
"OK...um...is that a strawberry or chocolate shake?"
"...what...?"
"Anything else?"
"You got my order wrong. I want..."
"That'll be three-fifty. Drive to the first window please."
The stupid thing is that it would be so easy to farm out the order taking to call centers, so people who are focused entirely on the customer, with no distractions, are the ones doing the communicating.
Yeah. This is my job these days. Generating a labour model that involves juggling independent tasks.
It does come down to definitions: if the employer is really asking the employee to
concentrate attention to two simultaneous activities, then the employer is going to see terrible results.
On the other hand, if the model is to ask the employee to initiate and monitor semi-autonomous tasks and to rotate attention among them, this does bring about efficiencies.
As a personal example, when I started working in food services it was an a bakery franchise ("Mmmarvelus Mmmuffins") where I was both baker and cashier. Once you've tossed a batch into the oven, it does not require constant attention. Just make sure you set the timer. If you have a customer at the till, they'll understand if you interrupt the transaction for nine seconds to take out a fresh tray of cherry chocolate.
The ability to rotate attention is built up with experience in that combination of activities. The new guy will perform badly. The seasoned guy will have enough spare time between attention demanding tasks to chat up the cute girl at the Orange Julius. Not admitting to anything.
Later when I worked on an assembly line, when I worked in a more sophisticated restaurant, and other positions over the years, the question was not whether there were efficiencies in attention-switching, but more about when one has found the limit and started to obtain diminishing returns.