Consider the following sentence:
I ate the sandwich quickly.
The word "quickly" modifies "ate the sandwich."
Should the adverb be placed up front, as in
I quickly ate the sandwich.
would it still be modifying the "ate the sandwich" part?
When "quickly" comes before the verb, it is a sentence adverb, and it means that only a small interval of time passed between some past reference time and the event of you eating the sandwich. When "quickly" comes at the end, it is a manner adverb, and it means that the process of eating the sandwich took only a small interval of time.
Although it sounds odd because of the repetition, it would make sense to say "I quickly ate the sandwich quickly." Consider a scenario in which you are in an eating contest, and after the starter's pistol, you need to dash to your table quickly and then grab the sandwich and gulp it down quickly. The first "quickly" modifies the whole sentence, and the second "quickly" modifies the VP.