Design used to be personal. Everything was designed for itself.
Now design is a bigger system. We often design for someone else’s layout and for different layouts simultaneously. Facebook designs their product, and inside of it, your design is part of their design.
Your choices only work if you consider theirs first.
Responsive design was similar. Layouts weren’t just layouts anymore. We gave up pixel perfect control to work within a bigger system. A design constraint.
Designing with third party social networks, ad networks, and sponsored content in mind is the next constraint. It makes design more homogeneous, but it also makes it more universal.