Before the visit
Clear a path to your attic hatch, basement and heating equipment, those are the three places the specialist needs to see. Grab a recent electric and gas (or oil) bill; usage history helps size the opportunity. If some rooms are always cold or hot, jot them down.
During the visit (60 a 90 minutes)
The specialist checks insulation levels, looks for air leaks, inspects heating and hot water equipment, and may install no-cost items like LED bulbs or advanced power strips on the spot. Ask questions freely, you're not being sold anything at this stage.
After the visit
You receive a report listing recommended upgrades with the Mass Save incentive already applied to each. That's when the real decision happens, and when air sealing at 100% off and insulation at 75 to 100% off usually make the choice easy.
The one mistake to avoid
Don't skip the assessment because you 'already know' what your house needs. The incentives are only available through it, and the inspection regularly finds issues homeowners never suspected.