Odd as it may seem today, many folks in rural areas are still using 56k. Others in rural areas are fortunate to have a-bit-larger providers that offer ADSL (utilizing two phone lines and two modems) to get a blazing 128k.
Others are use dishes and the various providers. A bit pricey.
The point is to be able to view your site as if you were on a dial up or slower connection. To test for performance, load time, etc. I know that alot of people are on broadband but also alot of people in rural areas are getting online with dial up, satellite and cell hotspots (all of which are slower)