To some this may be a pointless technique... but understanding how it works can mean the difference between understanding how a vendor's product is storing information and how it isn't. Case in point: a product we used to track web surfing suddenly switched from the a.b.c.d format for IP addresses (they were stored as strings... not the best way, but it was how it was done). We upgraded the product and suddenly the queries and reports started failing. Why? Because the vendor had converted the IP field to a type of integer format. Once you realized they were using bitmaps to store the IPs, it was easy to figure out the IPs and actually made reporting easier.

Also, using bitmaps can save on performance on the network side... think about all the field names, individual values, etc., that are shuttled from app server to database server. Generally it won't make a bit of difference because bandwidth is sufficient and resources are more than adequate, but there are rare cases where it can.