It may be a good security to generate 1'000'000'000 addresses to avoid someone to send your wallet over the web :p
Actually there's respectable cryptographic research into making signing keys enormous, potentially GBs in size. The purpose is to make it hard for a virus to steal them. Then you might say, well, how do I sign with a multi-GB key? This is the trick, you can sign using a small subset of the key, but the subset changes for each signature, so the virus has to steal the whole key in order to sign arbitrary data.
Not too applicable to Bitcoin, but the basic idea might be useful sometimes.