Recent scheduling heuristics for task-based applications have managed to improve their by taking into account memoryrelated properties such as data locality and cache sharing. However, there is still a general lack of tools that can provide insights into why, and where, di↵erent schedulers improve memory behavior, and how this is related to the applications' performance. To address this, we present TaskInsight, a technique to characterize the memory behavior of di↵erent task schedulers through the analysis of data reuse between tasks. Task-Insight provides high-level, quantitative information that can be correlated with tasks' performance variation over time to understand data reuse through the caches due to scheduling choices. TaskInsight is useful to diagnose and identify which scheduling decisions a↵ected performance, when were they taken, and why the performance changed, both in single and multi-threaded executions. We demonstrate how TaskInsight can diagnose examples where poor scheduling caused over 10% di↵erence in performance for tasks of the same type, due to changes in the tasks' data reuse through the private and shared caches, in single and multi-threaded executions of the same application. This flexible insight is key for optimization in many contexts, including data locality, throughput, memory footprint or even energy e ciency.