There are some guns that came with nickel plated magazines, and of course, guns that are nickel usually have nickel magazines to match.
The advantages:
Less chance of rust.
The "slippery" finish "may" cause the magazine to work smoother.
Disadvantages.
Bright nickel chips, cracks, peels, and scratches easily. Once compromised, the steel under the plating may rust. The first sign of this is when the finish bubbles up and flakes off exposing rust.
Magazines tend to scratch or scrape when inserted into the gun, and nickel will do so easier and worse.
The plating adds thickness to the parts. This could cause a tight magazine to NOT work smoother, or be harder to insert into the gun.
If left in a magazine pouch for a long period, the nickel may develop verdigris. This is the thick, waxy green stuff you see around brass or nickel hardware on holsters and other leather goods.