In a tweet from Gary Illyes, Google officially stated that 301 and 302 redirects didn’t lose page rank. This was not always the case. By the past Matt Cutts stated that 301 redirects did lose pageranks but then Gary Illyes explained that the Google logic has changed. Here is his response to someone who was puzzled about the statement.
HTTP to HTTPs
It is a very important statement because it means that redirects to HTTPS don’t lose google juice. Usually people used to link to HTTP version of a website. If someone decides to move a website to HTTPS, it should not witness a traffic drop.
subfolders to subdomains
Some people may have created 301 redirects to point from subfolders like /uk/ to subdomains like UK.domain.com. This would important to have no google juice leakage by doing such a redirection.