I'm no expert so please anyone correct me if I'm wrong, but the idea is
if you don't assign anything to a variable then there is a good chance that it will have some random value until you either assign a value to it or you initialize it.
example:
int x; // this x value can be 48484503023 or -234932493249 or some other crazy value by default
A followup question is: Has the class touched all the cases? I'd guess 'no'.
What is infuriating, is that some compilers in some modes do initialization that the standard does not require. That leads to unwarranted "But it works!" claims.
@Handy Andy
The “initialize everything” rule of thumb is a very good one to follow. It will save you a lot of grief. Some company code guidelines explicitly require it.