It is not a good thing because it is interest free and inflation exists. If you would have had that money earlier you could have put it in high yield saving account or payed down debt.
There are a number of different overpayment interest regimes[1]. Mine was paid based on time elapsed from the time of overpayment (overpaid quarterly estimated taxes).
I did not deliberately overpay as an investment strategy :-).
Last time I looked, you needed to be in a higher tax bracket than I was to make Muni bonds worth it, in part because my state (WA) does not have income tax. Something like the 35% bracket.
And anyway, my investment strategy is not long bonds at this point in my life.
