My rule of thumb is that each "hard pull" of my credit history causes about an initial 8 point hit to my credit score. That initial hit is reduced by about 50% after 6 months and then disappears after about 12 months.

However, if your credit utilization % goes down as a result of acquiring more credit, it could help your score too.

As was mentioned, even if it's a net reduction in your FICO score for a while, unless you're planning to apply for a mortgage or other loan sometime soon, it's often worth it.