Hey There I went on a safari it says This webpage is using significant energy. Closing it may improve the responsiveness of your Mac. So I am going to close it right away!
What does may means?
iMac 27″, macOS 10.13
The message is merely informative, and is intended for those who may not understand why their Mac is performing poorly. Not everyone is sufficiently knowledgeable to make that correlation. For example they might just complain their Mac is slow, and there can be a variety of reasons for that.
So I am going to close it right away!
Good, and then determine if your Mac is performing any differently — better or worse. Those are subjective impressions of course. For more qualitative measurements use Activity Monitor: Activity Monitor User Guide for Mac - Apple Support
If you are still using macOS 10.13 as shown in your profile information, you can expect its version of Safari will have a difficult time coping with websites that inexorably grow to become ever more resource-intensive. Website programmers are generally paid to show how clever they are. They don't care if their bloated web pages don't perform well for end users with modest hardware. End users don't sign their paychecks.
Safari is having Significant Energy Again!
