It's easier to maintain one calendar than a dozen. Some services allow you to publish calendars and contacts to specific users or groups. Others in your office can check your schedule or look up a phone number without having to interrupt you. Synchronizing with desktop applications. These services allow you to synchronize with your PIM so you only have to maintain one list.
Double entry is for aging accountants.
You automatically can send messages to group members reminding them you have a conference call in three hours or a convention in three weeks. Other handy features, such as private chat rooms, shared file storage, local weather forecasts and pager notification are available on many sites. There are easily two dozen calendars on the Internet. Like all Internet services, you should check a few to see which sites best suit your needs. The best sites offer secure connections.