Result source query difference between SPSiteUrl and Site

Working with with result sources and sometimes I see the query like this:

{searchTerms?} (contentclass:sts_listitem OR IsDocument:True) SPSiteUrl:https://example {?owstaxidLSTopic:{Tag}}

And other times like this

{searchTerms?} (contentclass:sts_listitem OR IsDocument:True) Site:https://example {?owstaxidLSTopic:{Tag}}

I can't figure out what the difference is between the two. I found this blog on the introduction of SPSiteUrl, but it doesn't address queries specifically.

Can anyone point me to a better resources that explains the difference between the two?