Technical apparel wicks away moisture and keeps you cool in hot weather and dry in cold weather.
Cotton shirts collect moisture and sweat resulting in a heavy/wet material. This combination causes you to become cold in lower temperatures and quick to tire in warmer temperatures. Chaffing of your skin is an undesirable side effect of wearing cotton during fitness activity.
Cotton underwear/boxers will become wet and heavy when combined with moisture and may lead to chaffing. Running shorts are lined with a brief or compression short made of technical fabric designed to dry quickly and pull moisture away from your skin. Technical running underwear is also available if you are partial to an added layer of protection.
Most people experience thigh chaffing when running/walking in cotton shorts. Compression shorts (which can be worn by themselves or under loosly fit shorts) provide the protection needed between thighs to avoid uncomfortable chaffing. Men and women alike experience this. Body Glide is a lubricated product that will protect any (and we mean ANY) part of the body that may experience chaffing.
Layering technical fabrics will ultimately keep you warm in extreme conditions. When air is trapped between wicking fabric layers the moisture is able to evaporate while the material protects you from the elements. A sweatshirt may keep you warm while it is dry, but just like a cotton shirt, it does not wick moisture from your skin. Technical jackets provide warmth, breathability, reflective elements and are coated in DWR to keep you dry in the case of rain, wind, and snow.