Minimal Download Strategy in SharePoint 2013 is one of the coolest features that got introduced in SharePoint 2013 and is enabled by default and can be disabled using EnableMinimalDownload property and settings its value to False. It improves client rendering performance and fluidity when navigating from page to page by download only the changes between two compatible pages. Fewer bytes will be downloaded and the page will appear more quickly.
In previous versions of SharePoint, unlike with Minimal Download Strategy,
when a user navigated between pages the entire page (chrome and content area)
were reloaded. Minimal Download Strategy significantly reduces the amount of
data that needs to be downloaded and reduces the amount of markup, css, scripts,
etc. that the browser needs to parse and render improving overall performance
and provides smoother transitions.
As previously mentioned, Minimal Download Strategy is made possible through a
new download manager that interfaces between the client and server. The download
manager understands controls whose display context is the current Url, controls
that can potentially change a Url (I.e. Quick Launch), controls that both have a
display context of the current Url and change change a Url (breadcrumbs), and
controls that do neither such as images.
Minimal Download Strategy uses a single .aspx file (start.aspx) for your
pages, with the actual URL encoded in the text following the hashmark (‘#’).
When navigating from page to page, only the changes between two compatible pages
will be downloaded.
The download manager follows a subscriber/publisher model therefore each
control must register its events with the download manager for example when
navigation download starts, ends, is cancelled, or fails. The download manager
is also responsible for managing the delta or the difference between the source
and destination page.