I never saw the point in that, but I know those who do. Prebaiting attempts to familiarize the rat with the trap by letting him crawl on top of it. If he's crawling on top of it, he can set the trap off and we can be done earlier IMO.
BOOM! winner winner, chicken dinner.
I followed a guy who pre-baited his cage traps for raccoons. He wired the door open. Told the customer it would take 3 days for the coons to get familiar with the trap before he could catch them. From day 4 to 14 he baited that trap every morning and fed the coon every night. IMO the coon had 3 days to "learn" that trap and then they didn't get caught.
I caught three coon in three nights in the same type trap, I just changed my bait presentation.
IMO pre-baiting is a waste of time and has the potential to make you look bad.
Now if you're fur trapping and pre-baiting before the season opens, well that's a horse of a different color.