'I will be singing'/'I will sing' proper expression?

I often hear native speakers saying 'I am doing Laundry this saturday' instead of saying 'I will do laundry this saturday'
I have encountered plenty more examples that native speakers actively use present progressive tense even though it seemed to me irrelevant to the circumstance the speaker is situated in.
For an another instance, in the voice class I once took, most students who were to perform their singing for midterm exam said prior to singing, "I will be singing "Blah blah blah". instead of saying "I will sing "Blah blah blah"." Whats the difference? This question might look stupid to you but I honestly do not sense the different degree of sensation each approach has. Please help me! Thank You!