The Function of Towers in the Book of Mormon
Towers in the Book of Mormon serve two main functions: war and religion.
Towers were used for public/religious spectacle(Helaman 7:10-11,14; Mosiah 2:7-8; Alma 48:1). Towers were also used as places of refuge(Moroni 9:7; Mosiah 19:5-6), surveillance(Mosiah 11:12-13; Mosiah 20:8), defense during war(Alma 50:4) and were desecrated by conquerors as monuments of their subject's surrender(Alma 46:36; Alma 51:20).
Torres in Mesoamerica served two main functions: war and religion.
Torres were used for public/religious spectacle(Codex Magliabechiano). Towers were also used as places of refuge(fortified temples), surveillance(high), defense during war(fortified temples) and were desecrated by conquerors as monuments of their subject's surrender(Codex Mendoza).
A Note on Words
Some might balk at the idea of equating temples with towers in the Book of Mormon, especially when towers are described as being next to the temple, but Hernan Cortez himself referred to the Aztec temples as "torres y mezquitas". That's because the Aztec temple, and mesoamerican temples in general, were "towers" with a "mosque" on top. This is also a nice example of semantic expansion. Everyone knows that the Aztecs were not Muslims but the Spaniards had just defeated the Muslims of southern Spain, in 1492. What else should Cortez have called the sacred building of, what for him was, an enemy culture?