Remember to back-up your files
Everyone should assume, no matter what their level of technical experience and knowledge, that their computer will fail at some point. Should you ever have to start from scratch, you can always download Stitchmastery again (we will happily help if you need to be resent your activation code, though if you have a Version 3 activation code you can check this in your Stitchmastery account) but if your chart, image, and stitch library files are only saved in one place, locally on your computer, they could be lost permanently if your computer dies beyond repair.
We would highly recommend you incorporate a system of backing up into your normal work routine. For example, you could choose to save all your files into a folder on Dropbox, Google Drive, iCloud or some other cloud-based storage or on a memory card or external hard drive. Or you can set a routine of backing up all your files to an external hard drive on a regular basis. There is lots of advice available on the internet to help you decide what will work best for you.
We would also highly advise that you hit save regularly when working on a chart, especially if it's a large file.
If the Preferences option 'Automatically create a backup file (*.bak) when saving' is checked then Stitchmastery makes a copy of the current file (for example - example.knt2) and adds a .bak file extension. Hence there is a copy of the file in the same folder as the original called example.knt2.bak. Stitchmastery also saves the changes to the current file. Thus example.knt2.bak would be a version of example.knt2 at the point that it was last successfully saved.
The reason for implementing this is that, if something happens to Stitchmastery at the point when it is saving any edits to the file on disk (for example, a power failure) then this could corrupt the file and all of its contents would be lost. This is a very rare occurrence but not a good outcome when it happens. This feature means that if it does occur, at least a copy of the previous version would be available that can be used to recover the file.