Quantum Leap was really just a twist on the classic Western TV formula of the lone stranger blowing into town, fixing someone's problems, and walking on to the next thing. Dozens of cowboys, a caucassian Chinese guy, a German Shepherd, and the Incredible Hulk all did it too.
I think the "swiss cheese" effect was mostly used as an excuse for Sam to not automatically use his genius-level intellect to know exactly what year and time he's in, not need Al to tell him all this stuff (and skipping all the usual exposition), nt keep trying to follow up on the stuff he'd just done when he next leaped, and not to have a reason to ignore the plot of the week so he can sit in a lab and try to invent a time travel machine again himself.
After he switched places, the SCE was restored. He *did* remember that he switched with Al once, but Al denied it - and Sam insisted he remembered so he could work out a time-travel shenannigan (I think with the Evil Leaper?). In any case, it's a plot device that helps move the story forward.
In later seasons they started using Al's future resources more often, from having additional people join him in the imaging chamber and help him out, to including the people Sam leaped into, in the actual plot. Once a guy even escaped from the waiting room (looking like Sam), and went on a rampage, forcing Al to head out to hunt him down. That was fun, and gave us a REALLY weird look at the year 1999, but was just a one-off.
Mark