question regarding reflect /refract interpolation

[chow choppe]

Hi all

 

i was going thru vismasters vray modules and i need to ask a few things regarding that

1.)In module 3 Brian is telling about using interpolation in materials.i understood that it can make rendering faster, but i havent understood exact use of it. i mean if its faster then why its not used in every situation.

So please point me to the right direction that when to use reflect and refract interpolation

2.) Also is there any information in these modules regarding rendering animation which has moving objects like cars etc.

 

Thanks