Pros:
- enhanced identification. A "damaged" but identifiable coin is almost always more desirable than an unidentifiable but "undamaged" coin. If a coin is so badly worn or corroded so as it cannot be fully identified, virtually nobody wants it since for just a little more money you can buy a worn but fully identifiable example. Using nic-a-date (or similar acid treatment) on a slick Buffalo is one of the very few examples in numismatics where "deliberately damaging a coin" can actually increase the information known about that coin.
- It's a gamble; you roll the dice, and you might "win", in terms of finding an actually rare or valuable date that would be worth considerably more than your original purchase price.
- You can fill in the empty slots in your album with coins you've found via nic-a-date.
Cons:
- an ugly, "damaged" coin is in your possession. Keeping it looks ugly, selling it can be tricky because only a small proportion of the coin collecting community is prepared to pay good money for a "damaged but rare" coin.
- It's a gamble; the odds of "rolling a win" are slim, and you're likely to have wasted time and chemicals for no benefit. Do it enough times and you'll eventually find a winner, I'm sure, but how much time and chemicals will have been spent finding it?
- It is irreversible. You can't nic-a-date a coin and then afterwards decide no, it looked better before, I'll undo that. Acid treatment has no "undo" button. Maybe in a hundred years time, coin collectors will all have "coin tricorders" than can scan a coin and read the hidden date of a worn-slick Buffalo without damaging it; those hypothetical people will surely curse your bones for needlessly and irreversibly ruining some of their coins.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis