Why do twitter servers make a request to the "url" that is tweeted in the Tweet button as soon as it is shared?

[Jatin2Tweet]

Hi,

I wanted to get some clarification here.
When I use Web Intents API or even pre-made tweet button from here - https://about.twitter.com/resources/buttons - the URL that is shared in the tweet message, is requested by twitter? meaning as soon as a tweet message is shared (and I know nobody clicked on the URL) but for some reason twitter makes a request to the shared url. I wanted to get some clarification as to why this occurs?

Thanks,
Jatin

[vincentisambart]

For example for Twitter Cards https://dev.twitter.com/cards
Even if a domain is not whitelisted it might be a redirection to a domain that is, so every page is requested. Also for preventing users to be sent to a domain with malware.

[niall]