Regular table salt is typically iodized and goes through a refining process to have a uniform shape and color. Kosher salt was originally made for “koshering” meats by drawing out blood from the surface of the meat without absorbing into the meat itself. This salt could then be washed off without adding too much saltiness to the flavor of the meat.
Both have close to the same chemical makeup (sodium chloride plus or minus some additives) but the biggest difference is the structure of the crystals. Table salt is highly refined and made up of tiny square crystals. Kosher salt is made up of larger grains, almost like flakes, that have been processed less.
There are several reasons to consider using kosher salt:
It’s worth noting that due to a difference in the density of table salt versus kosher salt, you can’t follow a 1:1 substitution ratio. 1 cup of table salt will be increase the salty flavor of foods much more than 1 cup of kosher salt. You typically have to double the measurement of kosher salt if a recipe calls for table salt. The larger crystals of kosher salt mean that you can pack as much into the same area as table salt.