"Keeping your balance as low as possible" is also not very good advice for another reason: just because bunq cannot immediately settle a charge with you doesn't erase your contractual debt. They could still ask you to pay up, just like most other companies that you have a contract with and where you are incurring regular charges would do when you just stop paying but don't cancel.
It's always better to actually cancel your subscriptions instead of just blocking payments, especially when you deal with legitimate businesses, as they could decide that you're still liable for some amount and even send it to collections or similar. Not saying bunq in particular does this, as I'm unfamiliar with their internal policies, but in general companies might do this.
