At first, yes.
But later on, it depends what classes you're taking. Once you start dealing with more complex algorithms or very large datasets, the time it takes to run your programs for a single homework assignment can start being measured in hours or even days. At least that's how it's been with my machine learning course.
Of course, chances are you'll have access to a department server to run this stuff on, but there are plenty of courses and situations in CS or physics that are extremely CPU-intensive. It's good to be prepared for that if you end up finding yourself interested in these areas. A netbook wouldn't even be able to load a lot of the datasets I get for my assignments into memory.
Of course if you meant the heavy lifting may not be done on your machine, then that's definitely a good point to consider. Personally, I like to be able to work on projects even when I don't have internet access.