The digital transition in educational testing has introduced many new opportunities for technology to enhance large-scale assessments. These include the potential to collect and use log data on test-taker response processes routinely, and on a large scale. Process data has long been recognised as a valuable source of validation evidence in assessments. However, it is now being used for multiple purposes across the assessment cycle. Process data is being deliberately captured and used in large-scale, standardized assessments -- moving from viewing it as a "by-product" of digital assessment, to its use "by design" to extend understanding of test-taker performance and engagement. While these techniques offer significant benefits, they also require appropriate validation practices to ensure that their use supports reliable inferences and do not introduce unintended negative consequences.