Should I set a custom promo code?

I'm new to rover, but I'm starting to advertise using things like business cards and social media. Before I order and design things like flyers, those tear-off posters, business cards, and other things that cost money and can't be changed later, I was considering changing to a custom promo code.

My question is, do you think it actually makes a difference? Either I'd make it my last name, which is admittedly somewhat difficult to spell if you don't have it written in front of you, or I'd make it some random word or phrase. Any suggestions or opinions???