It is like complete data... player fold and that's it. It is same as if the hand is played on other table and HERO don't sit on the table and therefore don't get hisotry for that hand.
It skew most of the opponents stats if there is a small sample size, but with big sample size the data will be close to the real and therefore still useful.
If all hands are imported, players will still be able to analyze their own game, check played hands, EV, winrate, redline, 3bet %, blind play and etc. If you stop importing all cash hands, this will be the same as no HUD and no Hand History for cash games.
Why not continue to support cash games with a note, that opponents stats will not be exact, but players can still use HM2 to track their play ??
I think that would be the better decision instead of stopping importing cash HHs at all.
Also if you start support HUD for alias (which is requested 4 years ago here -> merge hud stats of two players on two different sites? ), people who had older alias for the opponents (or accumulate nicknames over time) can add them and use HUD during play or when analyzing opponents.