ayrus2011
Well his action with the egg likely killed Fluffy since he wont be getting any secrets from Hagrid. Voldy likely didnt want to risk any notice using strong spells in there. Let alone right at the hallway inside of the school itself. Making money off the dragon would require it to grow up considerably. Until then it's nothing but another money guzzler. So if he wanted to help his cash flow all he did for some time was add another heavy expense. Keeping it wrangled, setting up an area that can contain it and feeding it.