Previously, these were hard-coded, but now it is possible to add additional parameters, or to change the hard-coded values.
Some use-cases that I have already encountered (there are no doubt many more):
The ability to set CURLOPT_STDERR (and to set CURLOPT_VERBOSE to true), to aid debugging.
The ability to set CURLOPT_SSL_VERIFYPEER to false if you don't have appropriate root CA certificates set up, or to set CURLOPT_CAINFO to an appropriate path if cURL isn't picking this up automatically.
Previously, these were hard-coded, but now it is possible to add additional parameters, or to change the hard-coded values.
Some use-cases that I have already encountered (there are no doubt many more):
Default behaviour is unchanged.