Warnings.

• Using a computer algebra system does not mean that you don't have to think. Most of the time, all works perfectly and you get the answer within 30 seconds. But sometimes, after 1 or 2 minutes, you don't get the answer or you get a Insufficient memory error. In this case, you should think ``Is there a different way to get the answer? Is there a way which will be easier for the system?'' And most of the time, there is a better way! Think of double integrals where you can reverse the integration order or define integrals where you may do a variable translation to have less variables, or linearity in inverse Laplace transform, ... You should learn math and algorithms to get the best of any computer algebra system. And a system is never complete, you will need to program sometimes!
• Most of the problems in the real life don't have exact answers but can only be solved approximately. Think of integrals, differential equations, large matrices (say e.g. 100$\times$100), ... Before learning how to solve exactly a problem, I strongly recommend that you learn how to solve numerically a problem. Then for a real life problem, you will know when you must stop finding an exact solution and begin to use a numerical algorithm.