Landmarked Properties

Isn't there an oversight committee, the landmarks commission, maybe, who oversees what changes are made?
That's actually a very good thing but many people wouldn't want to deal with that.

If you purchase something in a designated historic district or a property that has been independently landmarked you cannot make alterations to the exterior without prior consent from the LPC. Unless the interior has been specifically landmarked (which is rare in NYC), you can do whatever you want to the inside. It's really just the outside that the LPC is concerned with.

And for the OP, the pros are you would own something historically significant in a neighborhood with a certain amount of continuity and you can go to sleep at night knowing a developer can't come in the next day and blow up most of the block to build some huge glass box. There are also certain tax breaks for people who own designated properties. At the same time, the cons would be that you cannot change the exterior appearance of your home and your block is essentially frozen in time, preventing further development on a larger scale. It can also be harder to sell the property later on as there are only a certain amount of people willing to purchase something they know in advance they cannot alter or sell for development.