why don't we always use the latest .net framework? : <p>I am very new to DOT.net frameworks. 
Shouldn't we always update to the latest release?
List Entity framework or identity framework .. all those frameworks ... why do we keep them around? just use the latest ones. </p>

<p>In fact, I am just starting to develop an asp.net website with RestAPIs, login, register, social login... 
I wonder what is the best framework version (4.5) to use   </p>
