If you're familiar with front-end web coding, it's comparable to manipulating the properties of DOM objects vs. assigning an innerHTML string. Building a string is crude but sometimes effective - but when you want to really engineer something, you want to have every node made available as a data structure, since that puts it in a form suitable for algorithm design.

In a lot of instances, a macro isn't particularly more complicated in intent than a string + eval solution; it's just a much more verbose way of attacking the problem.