Personally, I use the WAIT function because sometimes the amount of time before the prompt can vary (especially if the message changes for holidays, weekends, or whatever). Then I get a pop up allowing me to simply press the trackball once to send the digit. You also will get the option to skip sending the digits which will return you to the regular "in call" screen.
WAIT means that the device will wait (indefinitely) for you to press the trackball to send the digits.
PAUSE will insert a two second pause for each PAUSE inserted and then the digits will be automatically sent.
Many people like the pause function. For me, I have often found that it can send the digits to so and requires some tweaking to get the correct length.