1. White opens up blacks king
2. Whites initiative continues
One side is said to have the initiative, or an initiative, when they are dictating the terms of the game to their opponent. The initiative may take the form of an attack, prolonged pressure, or even be prophylactic in nature. It can be the outcome of a positional advantage, big or small, or an aspect of compensation, either long term or short-lived.
In the above positions (Ehlvest - Markovic, 1998), white generated an initiative with 15.g4! (position 1), exploiting his lead in development and black's weak light squares.
After 15...cd 16.gf Bxf5 17. Bg4 (swapping off the bishop protecting the light squares, thus weakening them further) BxB 18. QxB Nc6 black had caught up with white in terms of development, only for white's initiative to continue with 19.h4 (position 2).