It's traditional to toast them (either over an open flame or in the oven) to make Mexican sauces like Mole and tamale sauce, but that may be because they're infinitely easier to break open and dump the seeds out. They become pliable, so you can stretch the wrinkly parts and get any hidden seeds, which are removed to make sure they don't ruin the texture of a smooth sauce. However, I do think it also alters the flavor of the chiles. I'm a purist for a particular regional preparation (I lived in central Mexico as a kid) and can't imagine not roasting them first.

toasting the red chillies, brings out a nutty aroma , but watch out, if they begin burn, it brings on a bad spasm of coughing & nasal irritation! i usually add a pinch of salt while toasting them (maybe because of a pure placebo effect, since i grew up with older women insisting that it reduces the cough & irritation!)

You don't need to, but that does sound good! Toasting chiles in a dry pan will coax out more flavor, just like it does for nuts, grains, and seeds.

I'm not sure if there's any science behind it, but I like to toast dried chiles in a dry skillet before soaking them. I think it enhances the flavor (by warming the oils, perhaps?), and it definitely makes the kitchen smell great!