The HTML5 <div> tag is the key in separating different partitions within an HTML document. This is necessary because it makes it easier for author to construct the document in an organized way. At the same time, the document will also be more user-friendly.
Formatting is easy with HTML5 <div> tag. It is capable of determining which group the block elements should belong to. Then, applying the style and format for this group is easier with the use of CSS.
For the comparison of HTML4.01 and HTML5, the only difference when it comes to the use of <div> tag is the method on how it is aligned. For HTML4.01, the align attribute can be used. However, this is already considered as obsolete. So, for HTML5, it is necessary to use CSS for doing this type of formatting.
Using the HTML5 <div> tag is not a problem because it is compatible with both the Events Attributes and Global Attributes in HTML5. All major web browsers are also attuned to the use of the HTML5 <div> tag.