Can sinus lift be done after the bone graft? Is it a common practice?

I had my tooth extracted and bone graft done on the same day. Initially, my dentist said, that I might not need a sinus lift, but today I had my xray done to see, how the bone graft is healing and he said that we need to wait for another 6 weeks and then he can determine, if the sinus lift has to be done,or there's enough space to put the implant in. The whole concept scared me a lot, as I have never heard of sinus lift being done after the bone graft is healed.