Chiming in because although Brian’s answer is good it spreads a for some reason rather common misconception about the soundpost. The purpose of the soundpost is not to transfer vibration to the backplate. In fact violin makers will put in the soundpost in such a way that the grain is perpendicular to the grain of the top to prevent vibration of the soundpost.
You can think of a violin a bit like a drum. You have got a frame with the top which act a bit like a membrane. Now what really moves the air is not the strings or the air within the corpus, but the vibration of this membrane.
The vibrations of the strings are transfered over the bridge onto the top, with two contact points (the feet of the bridge).
Now consider: If you have a string the bridge defines a fixed point where the string cannot move. This means that the closer to the bridge you are the less the string will be able to move. As lower frequencies require a bigger amplitude this means that the closer you play the string by the bridge the more high frequencies are favoured and thus the tone get’s brighter.
Similarly the soundpost acts as some sort of bridge for the top, that is a fixed point that prevents the top from vibrating at this point. Also similarly this means that the closer to the soundpost you agitate the top the more focus lies on high frequencies, the further you are away the more focus lies on low frequencies.
The combination of bridge and soundpost (and also the bass bar, which is another different matter) thus serves as some sort of eq that tries to favor high frequencies (giving brilliance, clarity and the ability to carry) for the high strings and lower frequencies for the low strings (giving body and fullness).
For this the soundpost is placed in such a way that it is slightly lower than the bridge under the highest string, somewhat shifted towards the second string. So ideally you get the shortest distance for the highest string, a rather short distance for the second and longer distances for the two low strings. Also there can be deadspots for certain frequencies.
Basically the soundpost can be moved in any direction and even small changes have a big effect on the sound and on the balance. It then requires a bit of skill and experience to tune it in a way so that it sounds good on each string over the whole range with a good balance while also matching what the musician wants.
So, backing what Brian said, the important thing is that the instrument and plays sounds good. If it sounds and plays worse than it did after a bump or fall it might be that the post as misaligned.
Also about that: A fresh soundpost sits very thightly and has the force of the strings pressing on it. As it is also very light it is very unlikely that it will be misaligned by some impulse. But over times soundposts tend to shrink a bit, which can make them a bit looser (especially when you take off the strings). This may then cause misalignments or even the soundpost falling over.