There are many different types and formats of resumes, and depending on a person's profession and the type of job they are applying for, different resumes might be required or preferred. However, in general, there are both pros and cons to a plain text or scannable resume.
One advantage of a plain text resume is that it can easily be copy and pasted anywhere. Many jobs ask that you apply directly on their site, and many want your resume to simply be pasted into a text box, which makes a plain text resume ideal; you won't need to make any changes, and there will be no changes automatically made to your formatting. If you have a formatted resume, however, and try to paste it in to a text box, the formatting could change and look unprofessional.
Another advantage is that plain text resumes are very easy to read. Everything is very clear and the person reviewing the resume will not feel overwhelmed or burdened by a formatted or fancier resume.
One disadvantage of a plain text resume is that it will be less unique and might not stand out s much as a personal, formatted resume. It will be the same font and color as all the other plain text resumes, which could make it harder to stand out or impress an employer.
A second disadvantage is that in a plain text resume it might be more difficult to highlight certain aspects of a resume that one could normally do by using bold or italics or underlining or changing of fonts and font sizes. In a plain text resume, it all has to be the same.
In general, one should think about the audience and mode of application in order to determine the best type of resume.