From time to time I have used Page Activate Peoplecode for page specific processing especially where page data/options would’ve needed to be reset or re-evaluated every time the page was loaded.
A while back I came across an article on Cedarhillsgroup website where Chris Malek suggested against using Page Activate PeopleCode. (Stop Using Page Activate Peoplecode)
While I still would use Page Activate PeopleCode, one of the good points he makes is the fact that Page Activate Peoplecode doesn’t activate when the component is invoked through a Component Interface. He suggests using Component PostBuild instead of Page Activate where it is applicable.
So stay away from Page Activate if you don’t have to use it, especially if you will be using the component in a CI.