CGMiner expiry and scantime settings

[CoinBuzz]

I found out i can set these settings especially in mining faster coins (scrypt coins).

I just want to know what these settings do? I read cgminer help but i have a question that for example if i set --expiry to 5, the miner stops to work at the current block after 5s ??

Also i want to know what is scanning in process of mining that i can set it with --scan-time argument?

How are these arguments affect my mining?

Note: I use cgminer for scrypt alt coins