Some airports have machines to wrap luggage in plastic. Now, security can open luggage to look into it for security reasons.
What does security do if they want to open a wrapped suitcase or box? Do they re-wrap it? Tape it?
As Mark mentioned it does depend on the airport and country, but as a general rule, the inspectors are only required to repack your items back into the suitcase they came out of. The plastic wrap is a disposable item and even if they slowly and carefully unwrapped it, it would be near impossible to rewrap. So plastic wrap would be tossed by any inspection after you have checked your bags.
If you have something like a cardboard box and the plastic wrap was keeping it shut, then the inspector would likely use tape to close the box after completing the inspection.