If you see in your backend metrics, that a button isn't clicked by a huge number of visitors you can start there and analyze. Common screen sizes are helpful, but more helpful is to look at the page since maybe other optimisations can be made, if that is the important button.

Similarly with languages, that you cans er from backend metrics.

More data seems always nice, but analyzing more data isn't making analysis simpler and there is a big privacy impact in analytics, especially when outsourcing to data collectors, who can gather data across sites. (Which then also gives Google information which services are interesting to user and can be integrated into search etc.)