The regular method requires you to keep the record and track for all revenue and expense transactions which involve GST/HST. At the end of the reporting period, the collected and paid amount of GST/HST must be re-verified and the difference belongs to the CRA.
On the other hand, you are not required to track GST/HST and do not claim an Input Tax Credit under the quick method. You just simply apply a prescribed GST/HST rate to the revenue you earn, that becomes the GST/HST payable for the business. With the Quick Method of filing HST you keep part of the HST that was collected on sales rather than remitting all to the CRA under the traditional method. The HST that you will pocket will be part of your income and you will pay tax on it.