In my corner of Amazon, PEs are the technical peer to high-level people/program managers. The people/project managers are there to make sure that human work proceeds according to plan and have small understanding or concern for nitty gritty technical architecture. In comparison, the PEs have small understanding of the nitty gritty of the human labor management and are there to drive design reviews and act as kind of a veto board for architectural decisions.

PEs rarely provide new ideas in design reviews (our product teams don't need help with that) but often will strike things down or modify existing ideas to fit in with other products, for business reasons, or perhaps because their human management counterpart doesn't like the idea.

Alongside, they usually have some variety of R&D style side projects that they pursue according to their interests/specialties.