Suppose you have a geared bike that you want to convert to a SS beater. Is there any functional reasons not to do the conversion the simplest way possible: stripping off the deraileurs and shortening the chain (leaving the crankset and rear cassette alone).

A few questions:
-can you do this with a bike with vertical dropouts?
-is there any reason to leave the body of the front derailleur in place (to keep the chain from jumping off the front chainring). is this even necesarry?
-i'm in the process of the conversion, and when i reconnected the chain, the pedals rotate when you walk the bike. Any reason why this happens?