As long as the "runners" don't gain enough height to limit you from lowering your light to the appropriate distance from the rest of the canopy, they are fine but too much height and you also have towering shade.. Imagine a triangle; the top of the triangle is the top of your cola, the lower portion, is the shade it casts (unless you have light from multiple locations covering the same space) the further the top of the triangle is from the bottom, the wider the base becomes. Of course this is not exact, nor is the shade created a perfect triangle as it depends on where in the "grid" its positioned relative to the position of the light but when the canopy's flat surface plane is broken, issues result (typically the colas next to it suffer at the lower portions)..Potential issues can simply be removed as to avoid effecting the overall harvest. Doing so however, is best when there is not going to be a hole left behind, as would be the case if in late flowering. Early enough, and you can fill the space with another branch or simply evenly space those in the area around it to fill it in. (Summer time: over crowding causes air flow issues and results in condensation which can lead to mold/mildew issues. Keep it even, thin if needed. If truely over crowded in a scrog, no amount of increased airflow will eliminate the issue completely before damaging the foliage)