It depends. For operations or aggregates on a single field, it improves cache locality, whereas if operations act on all, or most, fields of the struct, it hurt

It depends. For operations or aggregates on a single field, it improves cache locality, whereas if operations act on all, or most, fields of the struct, it hurts cache locality. The exact same tradeoff differentiates OLTP (transactional/row stored) databases and OLAP (analytics/column stored) databases.