John 20:7 ASV

I know for me, I tend to leave my bed and not make the bed or fold my towels or clothes. Perhaps this verse suggests that God is a God of order, and either one of the angels is a neat freak, or it's a good thing to fold your clothes instead of being messy.

Another thought: by folding the clothes, it shows intentionality that Jesus' body wasn't hastily stolen by thieves with malicious intention. A folded cloth is an indicator that they were not in a hurry to leave the tomb empty, and also to indicate this was the right tomb. If the tomb was absolutely empty, they may have found the wrong tomb since there were probably other tombs around.