[plt-scheme] cutting out of Interactions window

Earlier this month I asked about a mysterious phenomenon turning some of 
our students' .ss/.scm files from text to binary without their 
knowledge. It turned out they were cutting text out of the Interactions 
window and pasting it into the Definitions window, which resulted in 
snips being pasted; the snips have a binary representation (I understand 
this has now changed in the latest SVN version, but they're still snips, 
not plain text). In my relief at having found the cause of the 
phenomenon, I forgot to ask what the reason for this policy was. Can 
someone please explain it to me? Thanks. --PR