Checking in pages throughout the editing process is a critical step to web site maintenance in SharePoint. Not only does checking in your page enable other users to view your edits and/or make additional edits to the page, but it also creates a permanent record on the server that you can always restore if/when needed. Use Check In like you use Save in Microsoft Word – every time you make any changes to your page you do not want to lose, Check In.
SharePoint does have a Save option, which will save a local copy of your changes. Saving in SharePoint does not enable other users with permission to your web site to see your changes, and it does not create a permanent record on the server. If something happens to your system and you have only saved your work, you will lose all changes. Therefore, it is good practice to use Check In like you would Save in other applications, and to alleviate using the Save option in SharePoint altogether.