Caffeine is actually rather complicated when you look at he results for memory, learning and performance. Some studies show positive effect, some show none and indeed, some show a negative effect (your memory/learning/performance is worse). Either way, these effects are usually fairly mild.
If you are using it to enhance your performance, it might not be as great as you'd expect. If you're doing it just for this reason, i reckon you should just stay away from it. If you like the taste/enjoy it or anything else, it's probably worth it. Same for a day if you're dead tired you'll perform a little better (honestly, nothing replaces a good nights sleep though).
If you are not used to coffee and had a reasonable amount of sleep, i would absolutely not recommend you drink it before a SAC/Exam. The caffeine dose in coffee is rather high, for someone who is not tolerated to it, it will likely impact you negative rather than positively (anxiety/jittery/harder to focus).