What is Single Instance Storage in Exchange Server 2010

Single Instance Storage (SIS) has been in with Exchange Server from last so many years. As we know, SIS stores a single copy of attachment sends to the multiple recipients. For example, when we send a 20MB of attachment to 20 users, previous Exchange versions (before Exchange 2010) store 20MB of attachment once, even if there are 5 recipients. But SIS feature has now been removed in the Exchange Server 2010, which means Exchange 2010 will now store the same attachment 5 times (100MB for the database) and isn’t compressed. A side effect of removing SIS would impact on storage which would be 20% increase in the database size.