why Http Handler are used - Introduction to handler

 Http handlers are used for

Binary files

Dynamic image views

Performance-critical web pages

XML files

Minimal web pages

and these are fast and it only gives minimum response. example when you write  

Response.ContentType = "text/plain";

         //MediaTypeNames.Text.Plain

in aspx page it will give lot of information.

and when you write this in handler it will give only specific information that you want.

Also no return type of processrequest funtion in http handler

you can create other return type function in handler and also create model in handler.