Since Insync is a two-way sync, if you delete a synced file from one place it would also be deleted on the other. What would you like to achieve in doing so (ie clear cloud/local space)?
I would like to use my computer as the main directory storage. The Google Drive would be in effect my backup of my computer. If I delete a folder file on my computer, I would expect it to be removed on Google Drive, which I believe is what you mentioned as the answer.
So hopefully my document folder on the computer is the main one
Keep in mind insync isn’t really a backup solution. It’s primary function is to facilitate access across devices by ensuring multiple devices contain the same files/folders being synced.
Changes on any one device including in the cloud, replicate across all devices. This means if you delete a file on your local device it is deleted on all other devices including the cloud account. If you delete a file in the cloud it is deleted on all synced devices.
Another example, say ransomware on your local computer encrypts files currently being synced, insync will likely detect the files as changed and sync with the cloud, overwriting the files in the cloud and potentially on all other linked devices. Effectively you lose all data across devices.
You still should use a separate backup solution from insync.