Imbalance at the top of book has genuine predictive power over horizons measured in seconds, which is why market-making and short-term signals lean on it. Over minutes and hours it decays to noise.
It is also the most gamed statistic in the book, because displayed size is cheap to post and free to cancel. Treat a lopsided book as a hypothesis, not a fact, and check whether the size persists when it is actually attacked.
Example: 40,000 bid against 6,000 offered gives an imbalance of 40,000 / 46,000, about 87% on the buy side. Over the next few seconds the offer is more likely to be lifted than the bid to be hit. If the 40,000 vanishes the instant a seller arrives, it was phantom-liquidity and the signal was a trap.
Related: phantom-liquidity, depth-of-market, queue-position, imbalance-message