I find the neuropsych tests to also be very frustrating. You might be surprised though, sometimes the tests you feel you did the worst on turn out that you didn't do so bad.
Other times you find you've got a deficit you weren't aware of. Once they go over your results with you, if you have a problem they should help you with methods to deal with it.
Otherwise it's just good to have a baseline so when you think you're slipping in the future you can be tested and find out if you really are or if you're just paranoid.