I know it was to bleed through so the vote counters could abjudicate them

It's far worse than that. In AZ they also printed the ballots with the alignment offset (so the bubbles and text moves to right/up/etc). This meant that when they bled through the other side, they visually look like they aren't bubbling in something on the reverse, BUT the machine thinks they bubbled it in (because the machine doesn't look at what is printed on the paper, just where it expects the bubble marking to be). In the AZ testimony they were showing it basically caused Republican votes on one side to trick the machine into counting a Democrat vote on the other side (Democrat votes on one side turned into Independent votes, Independent votes got thrown out).