First sonogram at 6 wks

I'm scheduled to have my first sonogram at 6 weeks (currently at 4 weeks). Is this necessary? What are they looking for? My mom is a childbirth educator and she says doctors can try and push scans on you to help pay for their equipment and will play it off as "a chance to see your baby". (She's not being pessimistic or bitter, she just knows from working at health centers.)