According to Microsoft themselves, the performance mode can be used to optimize speed, response rate, memory, CPU and battery usage. How well the improvement is noticeable will also vary depending on the user’s surfing habits.
It is not entirely clear how the performance mode succeeds in this, but the mode should in any case use Edge’s sleeping tabs which will be locked for five minutes and make unused tabs not chew up performance in the background.
When performance mode will appear for all Edge users remains to be seen.
Also read: Child mode is coming to Microsoft Edge