Working people have a notion that work can be done on two or more things at the same time, thus increasing efficiency. But what we are actually doing is performing small parts of different tasks serially, alternating as we press each toward some result. People that are especially good at this can juggle more than two or three, providing the illusion that great quantities of work are being produced. Lots of noise and motion occur, as evidence of abundant zeal.
There is a price, though, as anyone who has waited for a harried receptionist can attest. The quality of the work can be greatly impacted by a lack of focus as people juggle too many tasks. In service work it can sometimes mean that conversations are abrupt and even rude. Often the server seems bored or hostile. I personally find it annoying when a service person can't be bothered to remove a telephone from his or her ear long enough to attend to a transaction. A lack of "gruntlement" on my part can sometimes follow.
This often occurs with the best of intentions, as we try to labor better by making ourselves attempt more work. A workday has natural stopping points that beg for additional load to be applied. Much has been written about "do more" techniques that wash in with the consulting tide and as quickly wash out again, displaced by the newest way of getting more done.
The reality is that we only really do this well when we have a very good understanding of how long a task actually takes. Breaks included. Downtime included. Maintenance included. Low esteem and motivation included.
The right amount of time to spend on a job is the exact amount that achieves the desired quality of output. Less attention than needed produces an inferior product. More attention than needed produces an expensive product.