web - When should I have addresses with #? -

when should have addresses # , when should have separate address each page or part of page.

for example

https://ca.news.yahoo.com/nick-hornby-boys-read-telling-101350029.html 

i know need have #, instance when call javascript method show lightbox(modal) websites using in unique address of pages.

for example icloud using show modal when click on create 1 now link.

https://www.icloud.com/# 

however, said websites using method have unique addresses pages.

for example following address showing single page of icloud website.

https://www.icloud.com/#find 

is correct follow practice of having # in our unique address of website pages similar icloud website has?

i not asking icloud.com thats example. meant if go www.icloud.com/#find page see not single page website because there header, login page , footer. why using #find , not find.html? there specific reason missing?

url fragments(#whatever) way address sup-parts of document. should keep in mind these never sent or seen server can't use them serverside differentiate between urls. can use them make parts of static page addressable or, right amount of js contortions, use them foundation addressable navigation within single page app. js frameworks rely on explicitly although starting go out of style browsers support history api.