When you unlink a Tiller Sheet it removes the sheet from your Tiller Console, and Tiller will no longer populate the Transactions sheet with new data.
Google Sheets will remain in your Google Drive, but will not longer be updated by Tiller.
Click the name of the sheet you want to remove to expand it's configuration.
Click Unlink this sheet.
Confirm that you want to unlink the sheet and disconnect the feed.