An interesting "interior" channel on the daily ES.
There are several uses for trendlines and demand/support and supply/resistance lines. The most obvious is to tell you in which direction you're going, up or down. And how fast. And sometimes a trendline can provide a trend "channel". This is determined by first drawing the trendline, then copying it and placing it parallel to the original line in a location where it coincides with what may be the opposite side of a channel. Oftentimes, this doesn't work. There's just no pattern. But sometimes it does, and this can provide clues as to effort, momentum, less obvious S&R, and potential trouble.
Here you have a channel that has been unusually predictable (though not at the beginning, of course). Note that after the channel became established, it found resistance at previous swing points, first at the outer edge of the wider channel, then at the outer edge of what has become an inner channel. Whether the channel lines themselves provide support or resistance is less important than their use in monitoring when and where demand and supply kick in.
To more closely monitor this, W also drew interim lines, such as the dotted lines drawn here. These provided an early warning if, for example, supply came in prior to price's reaching what had been the supply line. If price could not breach this line, this indicated slowing momentum and a possible turning point, particularly if other indications manifested themselves (such as longer-term resistance levels).
In this case, one can angle a demand line upward and a supply line downward into what pattern people might call a "rising wedge" (W wasn't into patterns). When price violates one of these, and it will, the fact of the violation won't matter as much as the manner in which the violation occurs, e.g., with high or low volume. In any event, any one of these lines can provide clues as to levels of support and resistance that might not be otherwise obvious.