A standard price chart shows the last traded price and not much else. Level 2 data shows the full order book, every resting buy and sell order at every nearby price level, which is a fundamentally different, more granular view of where real liquidity actually sits.
1. What a liquidity pool actually is
When a large resting order sits at a specific price, it functions as a pool of liquidity that the market will need to trade through. Depending on whether the order gets absorbed (filled and removed) or holds firm, price either pushes through that level or gets rejected by it, which is exactly the kind of information a plain candlestick chart doesn't show until after the fact.
2. The limits of trusting visible size
Large orders on the book aren't guaranteed to stay there. They can be cancelled the moment price approaches, sometimes deliberately, to create a false impression of support or resistance that gets pulled just before it would actually be tested. Level 2 shows current intent, not a firm commitment.
3. Where it's actually useful
Level 2 is most valuable for very short-term execution decisions, timing an entry within a few ticks, gauging whether a breakout has real size behind it right now. For a multi-day swing position, the order book will look completely different by the time the trade plays out, making it far less relevant to that decision.