Copper is a very reactive metal. At least compared to gold or silver. Could be lots of things. As far as effect on grade and value, eye appeal is very important to most buyers. Spots certainly aren't going to add any value. As far as detracting, are they subtle, or very pronounced. Limited to the fields, or all over the design?
Effect on grade is probably less of an issue. As I've seen very ugly spotted coins still grade high. Might knock it down a point or two if really bad, but still superficial. But a high grade doesn't really matter if nobody wants to buy it.
If the spots are more than superficial. Have damaged the surface under where they are, they yeah, probably a details coin, and a huge effect on grade and value.
If it's a high value coin, you could run it through one of the TPGs conservation services. Assuming the spots are superficial. But copper is kind of a crap shoot with that process. Can easily make the coin look worse.