Credit/No Credit Pro's and Con's ?

I'm a physics student taking probability. It's not required for my degree but I know that probability and statistics are good things to understand for experimental scientists, engineers, and perhaps everyone. Anyway, I wanted to get an A because I'd really like to learn it well, but after a few stumbles on quizzes it looks like it's going to be an uphill battle. Definitely still possible, but definitely not as high of a probability as I had originally thought (haha).

What are the pro's and con's of taking a class like this with the Credit/No Credit option? It feels like a cop-out, but it would also remove a lot of stress. I think that I could still be dedicated in doing the HW and shooting for A grades. It would certainly be a disappointment to earn an A but only get a "Credit" score; on the other hand, I'd like to get a 4.0 (it's my first semester as an MS student, I've got plans to go for a PhD somewhere else) and a B would be a bummer.

Any thoughts? Do Cr/NCr grades look bad to PhD programs? Is this is a common thing to do?

Thanks everyone