1. Non-registered accounts are very flexible. There is no contribution and withdrawal limit. If your TFSA or RRSP reaches the upper limit, you can use a Non-Reg account, while you need to pay taxes annually on income.
2. Non-registered accounts can be used reasonably with other types of investment accounts.
3. If your assets are in Non-Registered Accounts, you do not need to transition to RRIF when reach 71 years old.