Why would I use this module instead of viewfield?

I guess unless you plan to make additional manipulation via custom modules and themes, you might not particularly care how the data is actually stored.
The practical differences are immediately obvious from the interface, especially in the way that multiple values are treated. You can use autocompletes to find the actual view which may be beneficial if you have a lot of views. There is also the ability to provide arguments per each referenced view by delimited lists and PHP code. Additionally if a View provides several displays - each may be chosen seperately.
From what I gather Viewfield handles multiple values, and multiple displays, in a very different way, and rather than provide PHP abilities it uses Tokens (which many people prefer). Insert View is different again because it lets you paste macros in fields that are not specifically designed to show Views, and in places other than nodes.

I am thinking of creating a page here http://drupal.org/node/266179 but I will need some time to try out the similar modules to make sure I am being accurate about exactly what the difference is.

Here is a list of links I should go through before writing the article.

http://drupal.org/project/insert_view
http://drupal.org/project/viewfield
http://drupal.org/project/embed_views
http://drupal.org/project/viewreference
http://drupal.org/project/views_embed
http://drupal.org/project/views_attach
http://drupal.org/project/nodereference_views
http://views-help.doc.logrus.com/help/views/embed
http://stackoverflow.com/questions/247991/displaying-a-drupal-view-witho...

Well I didn't get enough material to really warrant a page, so I just did as you first suggested and updated the project page.

Also my information about Viewfield handling multiple values differently was outdated, they have now updated to use the same method as this module.

cheers