In the original pilot, Sheldon and Leonard go to a high IQ sperm bank in the hopes of donating their specimen to create intelligent offspring, but more importantly to earn some quick money. While filling out the forms, the two slowly change their minds and leave, never to really be talked about again.
The new oral history The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series by Jessica Radloff (via TVLine) tapped into all kinds of details about the episode, including that creator Chuck Lorre made sure that the scene was eventually cut out of the syndicated version of the pilot, noting that the show didn’t truly begin until Leonard and Sheldon awkwardly said hi to Penny while she was unpacking her boxes.
Although Jim Parsons defended the scene in a vacuum for the time-frame, he does agree with Chuck Lorre's reasoning overall, admitting that the episode works much better without it:
At the time, the sperm bank scene didn’t bother me. Looking back, it was out of place, but there was no way for the producers to know… Nobody knew who Sheldon was yet, so the live audience accepted it for what it was. But it is confusing information now, and I get why Chuck took it out of syndication because the episode is much stronger and more special without it.