The Priority System requires you to do just that, prioritize. Taking A in something means "I consider this to be the most important area of my character, the one that requires the most of my limited pool of starting resources." Taking A in something also means taking lower than that in everything else, and by the time you get to E you'll be feeling the pinch. So A priority in skills is a trap, if there is anything else that does more for the character as an A Priority. So you want to ask yourself "Do I need all of these skills? Will I actually use all of these skills?"
The book has an example of resources: A as a trap option. For a decker or a street samurai, resources: A is very useful. But for a technomancer? The character was buying things like 10 fake SINs, a deluxe DocWagon contract, an expensive SUV he didn't even know how to drive, etc. Obviously, that character didn't need that much in resources, and obviously, the character paid for it in other areas. The player probably had a lot of fun spending all of that money, though. That's probably why skills:A is taken when it is not necessary, too - it feels lavish. Suboptimal isn't always bad, though. If you can take a high Priority for something you enjoy but don't necessarily need, and still be able to get the character you want with your remaining resources, more power to you. But if you don't get the character you want, you might want to look at getting something more cost-effective for Priority: A.