Is there any argument against declaring a variable in C++ with auto? [duplicate]

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• How much is too much with C++0x auto keyword 13 answers

I find the auto keyword to be very useful as I don't have to worry about the type outcome of evaluating a complex expression or having to worry about which type to use (in terms of the right size) when initializing a variable. Besides backwards compatibility, is there any reason why I shouldn't use auto or circumstances in which it's not wise to do so ?