Whether toys, food, or data; sharing enables more than just one to benefit from something you or others posses. Sharing toys means playing together, which is just more fun. Sharing food means neither of us will go hungry. Sharing data means working together more efficiently.
Say I have a document or a spreadsheet or even a picture that you could really use to do your job. The same may go in reverse. To enable both of us to reap the benefits of any files or information that either of us posses we need to share. Simple sharing might be to email the file to you or place it on a CD or USB memory stick (not all that long ago it would have been a floppy disk) so you can put it in your own computer and use it. Sometimes that is all we need to do. Of course if either one of us changes the file, which is bound to happen, how does the other get the updated file? Whose is newer? Perhaps now mine has newer information than yours while yours looks nicer than mine. If only we had one file that we could share and work on together; it would be current and look nice.
That is one of the main reasons companies implement a data network. All of the computers and in turn people are tied together enabling an easy way to share files and information between everyone. This alone allowed for one of the greatest increases in worker productivity of the 20th century. No more running around looking for information and duplicating work someone else has already done.