You get bad-ass calluses. That's about it.
More serious answer.
Reasons to wear gloves:
- They can help grip if chalk is not an option in the gym. It increases the texture of your palm which will help stabilize the bar.
- They (help) prevent calluses. I personally am not against calluses, but it may be an issue for some people. Palm calluses can get pretty thick over time and requires sanding down or cutting.
Reasons to not wear gloves:
- Gloves can actually make gripping harder because it widens the grip of the bar. This could also be in the "reasons to wear" camp as it can be argued that gloves help develop more grip strength. There are better ways to do so.
- They can be uncomfortable.
That's pretty much all I can think about. It all comes down to preference. If you are ok with a few calluses, then by all means, skip the gloves.
Things are different for strength sport competitors however. Most federations in weightlifting, powerlifting, and strongman do not allow gloves to be used in competition, so you'll need to grip the bar with a raw hand. As such, you should always train without gloves in this scenario. Also you don't want the added disadvantage of the wider grip anyway.