Parallel Movement of Several Voices
Parallel movement of many voices usually sounds musically rather unattractive. Particularly if you let several voices leap into the same direction, the collective change of instrumental register will create a sonical disconnect that is usually not desired.
Try to avoid for example to move all string voices into the same direction on a chord change. These things can happen quite quickly especially when you’re recording several voices at once by playing them in on a piano. In general, the ideal situation would be to have an even spread of voices that move down, up and sustain over a chord change. As this ideal situation is not always possible (or desired) in the situation described above you should try to have at least one voice (other than the lowest) move in the opposite direction to compensate for the motion of the other voices. All that is of course covered by traditional rules of voice leading which however nowadays don’t need to be applied as strictly anymore. However, the general idea of these rules is an ideal that is still useful to be kept in your music.
As a side note: there are some arrangement techniques (e.g. big band block voicings) where it is part of the style to have a lot of parallel motion and some composers define their personal style by also writing a lot of parallel moving structures, so these things need to be seen with a a grain of salt. In general the rule applies: if you do it intentionally to create a specific effect, that is perfectly fine. However paying attention to try to avoid such parallel movement is in general a good starting point for a learning composer, arranger or orchestrator.