What is the purpose of not eating after noon? We all know this precept taken by the monks, but I would like to understand the reasons behind it. Currently the specialists claim that we should eat small portions every 3 hours or so, eating once a day is not a big issue, but is not recommended.
From my understanding, the Buddha laid down the rule to not eat afternoon in order to reduce the burden on the laity and to help the sangha avoid a negative reputation.

In the Latukikopama Sutta (MN 66) the Buddha said that there were many disadvantages to going for alms at night. 


  that monks wandering for alms in the pitch dark of the night have
  walked into a waste-water pool, fallen into a cesspool, stumbled over
  a thorn patch, or stumbled over a sleeping cow. They have encountered
  young hooligans on the way to or from a crime.