I had to do a certification for (two fast food establishments). I assume these certifications are for new people or when they feel the shopper may require additional training. I feel that it really helped in regards to getting my feet wet. It shows what to look for.
Mod note: Linking an MSC with its client(s) is a violation of Forum rules and probably also a breach of your ICA.
For that one, I was offered the certification after I had already done a shop. The way it was worded is that by being certified you were now a "premiere" shopper for that establishment. Since then I was offered those shops with bonus to do. I am guessing if someone else flaked. Doesn't hurt to have it.