Adobe/Macromedia Flash is and probably will always be an inefficient resource hog. However, sometimes there really is no other choice since some websites won't make an alternate version available if you're on a computer vs maybe a tablet
Adobe Flash Player For Safari
Simply having it installed probably isn't going to slow down your system any more than any other plug-in if it's not being used. But displaying Flash content is going use a lot of CPU resources. The worst is when you're viewing a web page with several ads (especially 'floating' ads) that each have their Flash content.
Adobe Flash Player Update For Mac Safari Download
Adobe® Flash® Player is a lightweight browser plug-in and rich Internet application runtime that delivers consistent and engaging user experiences, stunning audio/video playback, and exciting gameplay. Installed on more than 1.3 billion systems, Flash Player is the standard for delivering high-impact, rich Web content. The best alternative is to uninstall Flash from your system and download Google Chrome as it has Flash build into it and you're not vulnerable unless you're browsing in Chrome. If Safari is your main browser, as mine is, then you need to open Safari Preferences, go to Advanced and click the checkbox for 'Show Develop menu in menu bar'.