Mostly to protect my hands from calluses. Little more grip would never hurt anybody either.
If the gloves fit well, you'll get protection from calluses in certain situations, especially where something is sliding against your hands (e.g. pull-ups). In other cases, such as where constant pressure is applied (e.g. deadlifting), gloves don't help much, and if they don't fit well, can make things worse if the bunch up. Grip is also not straightforward. Gloves effectively increase the thickness of the bar (or whatever you are holding onto), so they can actually make it
harder to hold. On the other hand, depending on the material they are made off, they can make slippery objects easier to hold onto.
Depending on what your gym allows, I've found the following to be way more effective than gloves:
1. Let your hands toughen up. This takes time, but it's worth it: grip strength is one of the most useful types of strength on a day to day basis. And yes, the toughness of your skin is definitely a part of grip strength.
2. Take care of your calluses. If you shave them down before they get too huge or torn up, they won't be as noticeable.
3. Use chalk. Chalk helps grip strength FAR more than gloves.
4. Use tape. It can protect your skin from something "sliding" against it and you can get it to "fit" perfectly in a very thin layer.
5. Use straps.
Versa Gripps are the best, by far, although it seems like they have gotten very pricey. These completely protect your hands and let you "grip" far more weight than you normally could. Unfortunately, if you use them too much, you won't build any grip strength. Use sparingly.