Sierra was installed 4 weeks ago..cookies from a single site will sometimes number 24 all different..are these cookies resident in Sierra and only activated when you visit a particular site? the previous os "mountain lion" did not load dozens cookie

Cookies are bit of information that is required to view the website and they are always saved , the best settings is allow from websites I visit . Taking cursor on safari > clear history > clear all history and website data will clear all of your back history and website data that is saved , but it will be again saved when you visit websites in a normal browsing mode .

if you select always block , some websites could not work properly .

Read an article : Safari for Mac: Manage cookies and website data using Safari

If you are very much cautious and don't want the safari to store cookies in you computer use private browsing : Safari for Mac: Use Private Browsing windows in Safari

The OS in and of itself has nothing to do with the cookies a website puts on your machine. All websites will place cookies - some more than others. I selectively (manually) get rid of them about once a week (I use Firefox), but I have to be careful: one of my financial institutions' website will not recognize my computer if I accidentally delete their cookie and I have to go through a 30 minute phone call to prove my identity and get a temporary one time code so I can reset it. It's quite a hassle.

If you don't want to store cookies, set Safari's Preferences to never store cookies: Cookies and website data > "Always block".

Many sites won't work that way.