It does clean up easy, it usually costs a little more, and for cost reasons it may be available after brass has sold out. Anyway thats how I wound up with 100 StarLine nickel 45-70 from Midway this week (That is what was available). Personally I like nickel for the looks, ease of cleaning and sometimes separating loads.
There may be some merit to the idea of it dulling a case trimmer a little quicker and case mouth splitting a little quicker, but if you are not loading and shooting in mass quantity you will never know the difference. Side by side if the nickel is a SMALL cost premium above brass I will buy the nickel, cause I like the looks, but currently I buy what is avalable.
After the long, the short answer to your question is probably personal preference would be the key advantage. They are pretty though