By default all files in the workspace will be read-only. So when you want to start editing a file you will need to checkout the file. This is the best way of working if your IDE integrates with PureCM (e.g. Visual Studio or Eclipse).
If your IDE does not integrate with PureCM then it can be a pain to have to manually checkout every file before working on it. In these situations you should uncheck this option. This will allow you start editing files without checking them out.
When you have finished your changes you can then run the Check Consistency Wizard on the workspace to identify which files have changed. The Check Consistency Wizard is described in Chapter 11, Check Consistency Wizard.