This question may seem pointless for some people, but I think it actually may a real problem for space exploration.
Imagine an interstellar probe that is launched and accelerated up to 20% of the speed of light. This probe will aim at a planet that has been found in the Alpha Centauri system. If we don't want the probe to slow down, how can the probe launch a satellite towards the planet for it to orbit? If the probe zooms by at 20% light speed throughout space, it seems impossible!