Hello Stephan,
The tie points allows to select the image pairs that will be used for the depth maps calculation. If the number of the common tie points (inside the bounding box) is less than the certain threshold, then such pair will not be used for the depth maps calculation.
So if you have some points outside the bounding box - removing them after optimization wouldn't have any effect on the dense cloud. But if you remove the points which are obvious outliers or those that have very high reprojection error and then optimize the alignment, then it could improve the alignment accuracy. However, removing too many points may affect the further depth maps reconstruction, if there are too few points left in the box.