The Prusa3d knowledge base mentions that acetone will "rejuvenate" PEI in addition to cleaning oil and grease from the surface.
About once a week, or when prints stop sticking, use ACETONE to clean the bed. It removes grease better than IPA or Windex. It also rejuvenates the print surface. However, if you use acetone every day, PEI will become brittle and start cracking.
From a chemical or physical perspective, how does acetone affect the PEI surface?
Rejuvenate is probably a bit of an exaggerated term. The number one adhesion suppressor is grease. The stuff that comes off of the fingers used to handle the sheet. Even if you are careful and only handle the sides, the grease will be carried to the center of the plate next time its cleaned with less aggressive solvents.
Isopropyl alchohol does break down grease but not to the extent that acetone does. Acetone also attacks plastic particles that accumulate on the print surface over time.
PEI is resistant to a wide array of chemicals[1] including acetone but it can become brittle if exposed to it too much especially when hot so acetone is not recommended for daily cleaning.
[1] Ultem Product Broshure table 4-3
Acetone is smelly nasty stuff. Here's a sample recommendation for PEI maintenance from one of a few (million?) 3d printing help sites.
Use isopropyl alcohol, methyl alcohol, soap, Heptane, Hexane, or Naphtha. Avoid ketones (such as MEK) or strong bases (such as sodium hydroxide).
