A bar hides more than it shows

Two sessions with the same open, high, low and close can be completely different markets. One trended smoothly, one whipsawed six times. Your bar chart says they're identical. For anything holding longer than a day, that's fine. For intraday work it isn't, because the path determines whether your stop was hit before your target, and the bar has no opinion about order. This is the main argument for keeping finer-grained data than your strategy nominally needs: not to trade faster, but to know what actually happened inside the bar you're relying on.