Exceptions have a large overhead, and create larger binary and memory requirements.
I find it is actually easier to deal with errors without exceptions, and it takes more work and lines of code try catch statements then simply checking for error codes and such.
Remember, Qtopia and Qt/E are run in limited memory spaces.
As expected, the most important gain arises from the use of the -fno-rtti and -fno-exceptions options. The -fno-rtti option removes all code and data related to the use of the C++ run-time type information mechanism. The -fno-exceptions removes all code and data related to the use of the C++ exception mechanism (recall that the framework classes use a very restricted subset of the C++ language that does not use either the RTTI or the exception mechanisms). Taken together, these two options basically eliminate the overhead associated to the use of the C++ language.