I'd like to see you format a large document with tabs!
Imagine you have a 50 page document and each paragraph has been indent using the tab key at .5 inches. Then your boss tells you that the paragraphs need to be indented at 1 inch. If you used the tab key, you're going to have to add an additional tab to each of your paragraphs. But, if you used a proper indent, you could just highlight all the paragraphs and move the indent. But I guess you would call that "lazy".