-More Power used
-Could potentially shorten the life of the card
-Could make the card run louder (Depending on the cooling solution)
However GPU overclocking is a regular thing, it's how some companies even market their card e.g. *(Highest Overclock or Overclock Edition)
In most cases reasonable overclocking can boost the card's performance but it can get to a point where its just not worth it to overclock higher.
If you want to dabble in overclocking your GPU, I'd recommend doing a bit of reading to see how to do so and what kind of overclock is achievable
- Best of Luck