Sometimes it's needed to send the email based on the specific order status.
The simplest example would be to just setup the trigger that will send an email immediately, like this:
The more advanced use-case would be to check the order status after some time, and maybe send an email if the status didn't change (for example, if it's still "pending payment", send the instructions on possible payment methods).
Here's how it can be done:
If you setup the trigger to activate and schedule email only if the status is "pending payment", then after 3 days (if you set to schedule it for this period), it can check the status condition again and only send the email if the status is still "pending payment". If it'll be "processing" already, the email will be cancelled, so that way you'll be able to make sure the email is only sent if needed.
Of course, there are other use-cases like following up after purchase (processing/completed status in this case), and more.