Safari's excessive RAM usage limiting
By default, new windows and tabs in Safari are displayed in “Top Sites”, a 3×4 grid displaying those web sites visited most often with Safari.
'Top Sites' makes for a cute home page, but it will show sites one doesn't want showing up, and it will slow down Safari, especially on older computers.
This ostensibly useful feature is loathed by quite a few users because it slows down Safari and the system.
While there is no easy and 100% safe way to turn 'TOP SITES' totally OFF, a few steps listed below will help Safari's performance and lessen excessive RAM use:
Stop Safari slowing and consuming extra RAM (as it visits all the websites listed in Top Sites) by removing any and all webpages from Safari's 'Favorites Bar' periodically (every week or so):
Preferably, delete all webpages displayed within 'Top Sites':-
Safari > History > Show Top Sites —> mouse-over each page (not regularly visited) so that the 'Delete-X' appears in the top-right corner, and click the 'X' —
keep the iCloud page and the selected search engine for Safari, preferably Blekko (alt., DuckDuckGo, &c),
if and only if regularly visited.
Alternative method of deleting all the webpages within 'Top Sites':-
Safari > Edit Bookmarks > Favorites Bar —> highlight all bookmarks and folders —> Edit > Delete.
In this way, Safari's WebProcess component (an integral part of Safari's Sandboxing functionality) won't keep pinging those sites to download data (just to provide Previews of those sites); it's a known bug - missing parts of PerformanceNavigation & PerformanceTiming in the WebKit2 component of WebProcess used by Safari.