Some tax information (unused tuition and education amounts, RRSP limits, unused capital loss, and so on) get carried over from year to year. If your tax return includes these items, every year when you start a new tax return, you need to transfer this information from your previous tax return over to your new one.
While this can always be done manually, an automatic transfer avoids the possibility of mistakes, and is also faster and more convenient. This could be a major factor in deciding which product best fits your needs.
Having an easily accessible copy of your tax returns could prove useful for a number of reasons. You might need to refer to previous returns for things such as verifying your identity with the Canada Revenue Agency (CRA), or to reference as proof of your annual net income.
The process of viewing and printing past tax returns varies between TurboTax editions (instant access online, download of your tax data file required with CD/Download editions), and both can play a role in choosing a product that's right for you.
One of the major factors in deciding which product to buy involves cost. TurboTax products in each edition (online or CD/download) offer different value for your money, and calculating your cost-per-tax-return (dividing the price of a TurboTax product by the number of tax returns you need to file), can help you compare and choose products more effectively.