The CRA is doing more automated filing for simple cases, such as those who are low income, unemployed, only salaried, etc. One can accept or challenge their assessment, it's generally not complicated and unless you have write-offs they wouldn't know about or they made a glaring mistake, it's a waste of time.

For people with multiple income streams, high incomes, businesses and for those who did anything complicated such as moving for work, having a good accountant can net you thousands of dollars. Tax planning and optimization is particularly important for people as they approach retirement, it can save the odd wealthy person millions, no joke.