Lincoln Cents are zinc planchets plated in copper since 1982 and this process took a while to perfect. The plating didn't often completely adhere to the zinc planchet and so the air in these areas would expand and create bubbles of all shapes and sizes which look like freckles you are seeing. You can actually poke and burst these shapes and bubbles.
Once these pockets are breached it doesn't take long for the zinc oxide to form and eventually zinc rot to occur. Plating bubbles don't add any value to a coin, but collectors have paid a premium for them mistakenly because the coin was misrepresented as something else or the collector thought it was something it is not An extreme example of plating bubbling however might go for a few dollars on occasion, or such that it impacts the design in some way.