it is so convenient and save you money and time.
For example, you can skip the ticket line at the peak tram if you use octopus card. And they only charge your card when you scan it, 25 HKD for going up, 11 HKD for coming down, cheaper than ticket price at the window , and even better (no ticket wasted) when you decide not to take the peak tram down like you did. Buses, shops, even restraurants take octopus card. And when you are ready to leave Hong Kong, you can surrender your card and get everything back except 7 HKD (admin fee).