When to call Des() on an HBufC.

This is a common mistake. Des() gives you a modifiable descriptor, TDes, which itself derives from TDesC, so you can use it to call any of the TDesC functions. But it‚is unnecessary.

Here‚is an example of this common mistake:

TBuf<4> stackbasedFred(heapBasedFred->Des()); // Unnecessary, just use
it must be
TBuf<4> stackBasedFred(*heapBasedFred); // More efficient

further reading http://descriptors.blogspot.com/