Do I always need to have tracking enabled?

No, tracking is primarily intended to be active when a search for the device is needed.

While it is possible to activate tracking and leave it on at all times, the result is additional battery use since the GPS and wireless radios remain active in order to report their location. You can safely leave tracking off when it's not needed in order to conserve battery life.

Since you can enable tracking at any time from any web browser after a device goes missing, it's not typically useful to have tracking active at all times.