Some thoughts about what the standard provides by default:
by Andrzej Krzemieński
From the article:
The classes you design can do more (in terms of allowed operations) than what you could figure out from just looking at their member function declarations. The C++ Standard defines a number of cases where certain expressions involving your type are valid, even though there are no corresponding member function declarations. Sometimes this is just what you need; but sometimes the additional operations you never asked for can have grave negative impact on your program correctness...