The kijun-sen is the system's anchor. Price above it is considered constructive, and its flat sections mark price levels where the market has been in balance, which often act as magnets when price extends away from them.
A cross of the tenkan-sen above the kijun-sen is the classic bullish trigger, roughly analogous to a moving-average-crossover but computed from range midpoints instead of closes.
Traders also use distance from the kijun-sen as an extension measure: price far above it is stretched and has historically tended to revert toward it, though as with all mean-reversion observations, strong trends can stay stretched for a long time.
Related: ichimoku-kinko-hyo, tenkan-sen, moving-average-crossover, mean-reversion, kumo-cloud