If you're working on a file on your machine and at the same time a colleague is working on the same file in the cloud or on her machine, which changes are saved? When a conflict like this occurs, Insync will notify you via the Conflicts tab so that you can decide which changes to keep.
Either way, you have no data loss.
You can either keep changes you've made while working on the file locally and upload it to the cloud or you can choose to keep the changes you've made while working on the file in the cloud and sync it to your local machine.
Once you've made a decision, a notification will appear on the Activity Feed informing you of your choice.
If you find that you often get file copy conflicts, you can save time by choosing a new default option from the Settings tab.