Its the principal of the thing! I chased €100 outstanding for nearly a year - it almost certainly cost me more in time & fuel than the money owed, but the satisfaction of finally getting paid really made it worth it.
I don't mind when ppl genuinely can't afford my service - in the current climate I've lost a few to that & appreciate their honesty in telling me. The ones that know they can't pay but don't cancel & don't pay really get on my wick!