The shared Daily Challenge is useful when you want one common board and a leaderboard result. Unlimited play serves a different task: repeating the same four constraints until scanning rows, columns, colored regions, and touching cells becomes faster and more systematic.
Use smaller boards for a short warm-up, stay in the 7×7 to 9×9 range for everyday practice, or move into 10×10 to 12×12 when you want a longer deduction chain. You can change size or request another board without waiting for the next UTC day.
Practice deliberately by finishing several boards at one size and watching for recurring region shapes, then change size when you want a different scanning load. Size changes how much of the grid you must track, but it does not guarantee a particular recorded difficulty.