Why calluses happen
Calluses are thickened skin that form a barrier to friction and pressure. When a particular area is exposed to frequent excess friction or pressure, the skin cells of that area react by forming links to each other via a network of proteins and fibers of keratin.  This prevents the skin cells from falling off as quickly as they would normally in other areas and the thickness of the skin builds over time.
The skin requires frequent insults of pressure and friction to continue building that fibrous network over time, otherwise it will try to conserve its energy by reverting to its normal thickness and sloughing.
When too much friction occurs over a time period that is too quick for the skin to form a callus, blisters occur.
I think it is so cool how the body can adapt so specifically and precisely to exactly what that person does frequently. It is so precise that it doesn’t waste any energy building up that barrier even a quarter inch away, only exactly where it is needed.
Benefits of callouses
Again, calluses act as a barrier. They protect the necessary, functional tissues underneath that area of skin from forceful pressure and friction (which is really just pressure that is moving).
When pressure is applied, tendons and muscles can’t move well, blood vessels collapse and can’t move blood, and cells of all tissues can die. As callouses form a thickened and more rigid layer of skin, that pressure gets spread out between a larger area underneath.
This distribution of less pressure means the insult doesn’t prevent function or cause cell death. Muscles, tendons, and ligaments can move better. Blood vessels can get blood where it needs to go. And skin cells don’t die off causing injury and infection.
Why we want to get rid of calluses
Calluses are primarily bothersome because of aesthetics. For weight lifters specifically, calluses of concern tend to be on the hands. In our daily lives, our hands are uncovered and exposed frequently to those around us. We even shake hands causing them to not only be seen frequently but felt also. Many are self-conscious that they give an appearance of poor grooming and self-hygiene.
Additionally, when calluses become dry, they can peel and crack. These rough edges can easily catch on the rough edges of objects we use. The callus will split or peel back, causing pain, bleeding, and high risk of infection.
Dangers of getting rid of calluses
The main danger of getting rid of calluses is that all of the benefits of protection they provide are lost. Skin breaks down under friction and causes pain and infection. Muscles and tendons cannot move well and can tear. Blood vessels collapse and do not allow blood to provide the healing and nutrients and waste removal it is supposed to.
Using pumice stones to remove the skin is also dangerous as it is not very precise and it is very easy to accidentally cut open the thinner skin next to the calluses when trying to shave down the callus. This also opens skin and increases risk of infection.
3 Steps to soften calluses instead
Instead of using pumice stones to tear away layers of skin, what I do is soften my calluses instead, primarily with Argan oil and shea butter.
Every night before bed, I use the following 3 steps:
1. Argan Oil
I first massage in 4-5 drops of Argan oil to my calluses (and into my cuticles). Any Argan oil will work but I found this to be the least expensive and this is the one I use:
2. Shea Butter
I next apply shea butter all over both hands to seal in the Argan oil and provide further softening. Again, any shea butter works but this is the one I use. (Yes it is labelled foot cream and I use it on my hands but it’s just shea butter so it can be used anywhere.)
I then cover my hands with these gloves to keep the oil and shea from rubbing off on my sheets overnight. Again, any light gloves will work but I like the touch screen gloves because I use my phone as an alarm and usually set my alarm after putting the gloves on as well as needing to turn the alarm off in the morning quickly and I don’t want to take the time to take the gloves off first (alarms suck!)
Help Prevent Calluses in the First Place
I love this infographic about preventing calluses. This only works for pulling exercises (like pull-ups, rows, lat pull-downs, etc) but I have found it helps significantly. It gives you slightly thicker calluses right below your first knuckles but I like the way the calluses are more spread out.
 Greenberg CS, Birckbichler PJ, Rice RH (Dec 1991). “Transglutaminases: multifunctional cross-linking enzymes that stabilize tissues”. The FASEB Journal. 5 (15): 3071–7. PMID 1683845. https://www.ncbi.nlm.nih.gov/pubmed/1683845