well most of the leathers now a days are built with vents, etc to keep you cooler, but that is usually the concern. Leather doesn't breathe as well as textile . Its also more expensive, and wearing it in the rain is a BAD idea. if it gets wet it will bleed and smell.
BUT it will also last longer and typically offers better protection. Leather is bar none the best protection on a bike.
Textiles offer just as good protection, but usually sacrifice weight and size. you need more padding and layers. they are really only designed for ONE crash, also. where as leathers can very well last you a couple spills and come out just a little worse for wear. Textiles are like todays modern collapsible frame cars (they are made to keep you safe, but the unit itself will usually be destroyed) whereas leathers are more durable like the steel frame behemoths of years past.
There are a lot of good leather/textile combo's out there too!