Answer:
When you need to keep the original document or send the document to multiple people.
Explanation:
If you need to keep the original document (eg. marriage documents or birth certificate or something important), you would make a copy of it (unless you are sending it to a lawyer or a government agency).
If you, for instance, have a memo for your company that all your employees need to read, you would copy the document so you would be able to print it and send it to everyone without passing the document one at a time.
Yes. Originally ARPAnet (Advanced Research Projects Agency) was conceived as a network between large universities, the government, the military and government contractors. Basically a bunch of friends and aquaintences. Security really wasn't a consideration until after ARPAnet was opened to the public.
SSIDs and Physical security
It is always recommended to have separate networks. And in this case, the SSID (Network Name) of the guest network should be separate from the main network. It is best to enable a guest account on your router and assign a new SSID. You can leave this network open or password-protect it. Visitors will be locked out from accessing the main network’s devices like printers and other sensitive information.
Physical security.
In terms of a secure network, nothing is safer than having your guest network installed on a separate hardware. By having a few access points set up for the guest network, your guests could entirely be segregated from the main business network.