You can click on the checkbox with your right mouse button. The program will tell you, what this option is for.
If you don't use DVDs from another region, there is no much use to activate it, as CSS cracking is very fast.
As far as I am aware, when you use the archive, the prog will use the archive when you put a dvd in that you have already backed up. It makes it quicker that's all. CSS cracking has nothing to do with region encoding, that is a completely different thing!
Update;
Just checked on my AnyDvd, I was correct in my assumption!
> CSS cracking has nothing to do with region encoding, that is a completely different thing! <
It has, trust me. If you have a RPC-2 drive and you want to play/copy a disc which is CSS protected which has a different region, AnyDVD must perform a brute force attack to crack the CSS keys, which may take a minute or two (worst case).
In this case the CSS archive is a saviour, as it will take no time at all the next time you try to read this DVD.
If region codes match AnyDVD will always be ready within seconds as no brute force attack is needed.
Conclusion: If region codes match or your drive is region free, this option can stay off.