DSL Filters ?

[Andre Kesteloot]

Gang,

DSL Line conditioners, or filters, are installed between the incoming 
telephone line and each telephone set. The blurb states that "the 
in-line DSL filter eliminates all erratic impedance from telephone 
equipment that interfere with DSL".
See for instance:

http://www.suttleonline.com/pdfs/900SeriesAdapters.pdf

Does anyone actually know what this is supposed to mean?
73
André