Q:

Cover page: is it ok to start subtitle with dash?

By far most of the research reports I read that have a subtitle start the subtitle with an uppercase letter (figure to the left below). Is there any reason why the subtitle should not start with an en dash and a lowercase letter (right figure below)? 

A:

There are multiple reasons why the example on the left is better than yours:

First is the issue of capitalization. You're advocating to lowercase the U in Understanding which goes against Title Case.
The next is that the en-dash holds a similar function grammatically to a comma. You would place this punctuation at the end of the top line, not the start of the bottom line.
You're treating it as though the Title + Subtitle combine into one cohesive sentence. If that is the case they need to be a complete sentence including period at the end. You'd also need to make sure that all titles and subtitles can be treated in a similar way.

