Check it if you want Tone Generator to play the last tone loaded from the previous run.
The sample rate of the tone which you can choose from the drop-down list.
From the Tone Interval section you can specify the step the frequency of the tone should increase or decrease when you chose to increase/decrease from either the menu or the small toolbar, or when you press +/- on your keyboard. The step can be specified in Hz or in integer multiples of semitones (up to 12 semitones per step).