My rule of thumb is to name everything. Not every header file has nice comments before each function, and therefore the parameter name is all that remains to decipher the function when there is a lack of decent documentation.
In the worst-case, it's a bit of extra typing on the behalf of the programmer. It shows intent, in addition to any comments that have been provided. I have never, ever been one to advocate a practice that seems to exist purely to save typing. In these days of auto-complete iDEs, it's never been easier to be verbose.
