I am not a financial expert, but I will just share my personal experience.
The answer really depends on if you are reliable at paying your credit card bills every month or not. But for me, I open cards strategically to benefit from their sign up bonuses and their cardmember benefits, and I pay off the entire balance of every card every month. I never pay interest or late fees of any type.
In the last 2 years I have opened 4 new cards in my name, in fact all of those cards were opened in the past ONE year. My credit score is currently 796 which is in the top range for a credit score of A . Could it be higher? Yes. The scale goes up to 850. Am I worried about it? No! This is a great credit score. I will continue to open new cards to get free travel and maintain an excellent credit score simultaneously. It's all about being a responsible credit card user. Don't overspend. Don't max out your cards. Only buy things you would already buy.
Doing this has saved me an immense amount of money on flights and hotel stays. If you would like to see the cards I am currently using to achieve this, click here or visit the "Get Free Travel" tab.
Free Credit Score: Compliments of my Chase Credit Card Dashboard!