Question: how do i know if i need to replace drywall?
Answer: Holes. Small holes and medium sized holes can be patched up, although the patchwork will almost always remain slightly visible. ... 
Water damage. Not all water damage will require replacing drywall panels. ... 
Cracks. Cracks are a good indication of a misplaced seam. ... 
Splinters. ... 
Bumps and bulges.