I'm new to this credit card churning idea and had a question regarding downgrading my card.

I'm looking to get a card for cashback / rewards on Grocery purchases and the Amex Blue Cash Preferred offers the best (6%).

The card comes with a $75 AF (waived the first year) and being a single guy in my early 20s, I don't spend enough on groceries to justify the fee past year one. I'm better off with the 3% that the Amex Blue Cash Everyday card offers with no AF.

After doing some research, a lot of websites/blogs suggest getting one of these 2 cards for groceries. My question is, why would anybody NOT sign up for the Preferred card, take advantage of the better sign-up bonus, and then downgrade before the AF fee hits?

Does that hurt your credit? Will Amex look at it negatively in the future?

Thanks