Long dog nails aren't just an aesthetic issue, and neglecting to properly take care of your dog's nails is one of the most overlooked problems in the world of dog health. The general rule is that if you can hear your dog's nails clicking on the floor or pavement, they are too long. Here is why: When nails are so long that they constantly touch the ground, they exert force back into the nail bed, creating pain for the dog (imagine wearing a too-tight shoe) and pressure on the toe joint. Long term, this can actually realign the joints of the foreleg and make the foot looked flattened and splayed.
Compromising your dog’s weight distribution and natural alignment can leave him/her more susceptible to injuries, and make walking and running difficult and painful. This is especially important in older dogs, whose posture can be dramatically improved by cutting back neglected nails.
Long nails can get torn or split, which is very painful and, depending on severity, may need to be treated by a veterinarian...
Remember that dogs express pain differently than humans. Dogs aren't complainers so don't wait for them to limp or yelp to take care of them! I personally grind my dog's nails because I don't want to ever clip the "quick", which continues to grow with the nail. Let me know if you'd like help figuring out the best plan of action for getting those nails down!
source: Whole Dog Journal