Most computer manufacturers have multiple tech support tiers, which include end-user support and authorized service provider (ASP) support. Authorized service providers can do more complex repairs, such as replacing laptop screens, motherboards and such. It used to be that in order to talk to ASP support, one would have to be certified by the manufacturer in order to get the (supposedly) higher level of support. The A+ certification came about as a way to simplify the process. Some manufacturers now accept A+ certification sufficient to get ASP support. (Provided that you actually work for an ASP, that is.)
I took the test years ago when it first came out, and I passed it without studying, but I had quite a bit of experience at the time. I know that it’s changed at least once between then and now, but I have no idea whether it’s more difficult or easier now.