Personally, I focus on the total bitswaps per minute graph across all the tones to give an indication of lines that need it & those that don't.
Almost all connections need DS bitswapping to some extent & some need it more than others.
With VDSL2, if a connection also needs a lot of US bitswapping, it is often an indication of either a very noisy connection or that a potential physical cabling issue is brewing.
I have attached a graph showing 24 hours worth of bitswapping from my own 1100m long VDSL2 connection as an example.
Just for info, DS bitswapping per minute before the 2013 HG612 modem firmware update was at a much lower lower level (see the other attached graph).
Increased DS bitswapping was a definite improvement, certainly for my connection, as it actually reduced error counts & improved stability.