I know it can be iffy to compare ordinary mail to email. But, here goes.
Before delivering the mail on any given day, one of the first thing the Post Office does is sort it. Each address’s mail gets grouped together so that it can be delivered in order.
But imagine what would happen if, when the postal worker was out the door and half way to your house, they called him back and said “Oh, new mail just arrived for Fred Smith! Come back and get it so you can add it to your pile!” Since new mail is always arriving, the poor postal worker would never get to actually delivering any of the mail.
There is much wisdom in batching things. Things that make it into the batch get done with the batch. Things that arrive during or after, get done in the next batch — not added into the current batch right away.
Here’s the interesting thing: In the scenario above where the postal worker continually goes back to get the new mail, it’s not as though the mail volume is any higher. He’s not prevented from actually delivering the mail by the fact that there is “so much.” He’s prevented by his process; by his approach. In the batched approach, there is just as much mail. It just happens to actually get delivered.
I realize that there are limitations to this. But the general principle is very useful. If you check your email continually, you’ll never make progress on the other work that you have to do — or on the tasks that your email has generated which have to be done outside of email.
Is “never” an overstatement? Well, a bit. But you get the point.