You're in the middle of composing e-mail when a warning pops up, telling you that you will be logged out due to "inactivity." It screws up your message, because you might not notice that the last few keystrokes weren't typed in your message window. ISP programmers are notoriously ignorant about detecting keyboard interrupts or determining when the active window contains an e-mail editor.
On the other hand, Internet communications, whether manual or automatic, seem to be sufficient to convince the ISP software that your session is active. I've occasionally run my HSPost software overnight and had it run to completion, except when the call was eventually dropped by the phone line after several hours of unattended execution!
HSPost is just one example of a spider or robot application. You can have all kinds of useful tasks going on automatically at the same time you're browsing the Web manually. Learning to write spider software is a lot of fun and very rewarding. To learn more, click here!
DISCLAIMER: If your access software has an option for limiting your session time regardless of activity, you will have to modify the setting. Otherwise, even running a robot application may not be sufficient to keep you connected.