The idea isn't to date each verse, or passage. The idea is to reconstruct a sequence of events which occurred in actual history, during Jesus' public phase - a sequence which can then be viewed as [a part of] the broader context of all Jesus' actions and sayings, first as a whole, and then perhaps somewhat developmentally.
In how many ways was his final year of traveling & preaching at all different from his first? In how many ways did his strategy change after John's arrest, and after John's death? What, if anything, does that say about Jesus' mission *before* his Passion took place? Does a brief (1 or 2 year) ministry support those who want Stephen and Paul to get on stage as quickly as possible? Does a longer (3 or 4 year) ministry require us to consider more carefully that God may have wanted something from Galilee and Judea, also?
The idea isn't to reconstruct a context for reinterpreting particular sayings and actions of Jesus. The idea is to care about the fact that Jesus' enormous impact on his own day didn't take place in a chronological or developmental vacuum. The idea is that some event-based context is better than none. The idea is that sequenced events tend to influence one another. If Jesus' actions stay in the Gospels, they remain that much more insulated from the book of Acts.
Why don't Christian believers put more effort toward reconstructing a History - an historical synopsis of Gospel events?
To date, I still can't think of any good reasons not to.