It is the first sign that a trend must be near to its end.
It is the first entrance of large, well informed traders against the main trend.
In other words, it is the first attempt of well informed traders to absorb orders.
Before accumulation the preliminary stop called Preliminary Support or Preliminary Demand.
Before distribution the preliminarily stop called Preliminary Supply.
Preliminary Stop usually display in two different form:
Narrow range candles with high volume (Which is also a sign of divergence).
Long tail/wick/shadow candles with high volume.
Uses of preliminary Stop:
It is an indication that trading in the direction of trend is not a good idea anymore.
The current market level might be a good place to book profits from previosly open trades (if any).
Extra Info:
There is a possibility for a trend to have multiple preliminary stops before entering into a clear sideways direction.
Due to inertial movement (Go with Flow) of a trend, trying to stop a trend is just like trying to stop a cargo ship. (A lot of power is required).
So sometimes one preliminary stops may not be enough.