Filtering Non-xDSL Incoming Lines

Just in case anyone reading this has more that one line coming in to the premises, it may be worth putting a filter on other incoming lines, even if not used for xDSL We have two lines coming in to the property, and putting a filter on the non-DSL line made a noticeable difference (~0.5dB) in the SNR of the VDSL connection.
I presume it prevented interference from the in-house extension wiring of the non-xDSL line getting back into the cable bundle and thence being coupled into the xDSL line.