As a user, what are the drawbacks for Interac e-transfer auto-deposit and what I should consider before using it?
About the only drawback is that you can't choose where the money goes. My son in law has only one bank account; he has auto deposit on. My daughter has several: one with the bank that holds their mortgage, one with another bank that is her general purpose operating account, and of course a savings account. She might want to deposit an e-transfer into any one of these accounts, so she doesn't use auto deposit and she makes the choice each time.
If you only have one account, there's no downside; go for it.
Kate's answer is good, but there is one other scenario where this may be disadvantageous. You may or may not want to actually accept the Interac e-transfer... Perhaps someone has sent you too much money (say a friend) or someone has not sent you enough money (perhaps relating to a business transaction). Automatically accepting the money may commit you, to some extent at least, to something you hadn't agreed to.