Many short-term teams are sent in support of long-term efforts. Short-termers often pass out tracts, do street evangelism, build houses, run clinics, do programs with kids, and other very good "seed-sowing" efforts. In this context, short-term efforts can be incredibly helpful.
However, many short-term efforts are directed at places with no reference to long-term efforts whatsoever. People "make trips," "tract-bomb," go on spiritual pilgrimages and the like.
Such a short-term effort may make a difference in the life of a few people. But it is really more akin to a nomadic, wandering farmer who flings out seed but never comes back to inspect the results.
"Johnny Appleseed" is a popular legend in American folklore: a kindly, almost dreamy man who wandered the countryside of America, flinging apple seeds randomly everywhere he went, so the apples would grow up into trees and everyone could eat. You can see elements of this legend coming out in the way people describe how they are "sowing seed."
But the legends are wrong. "Johnny Appleseed" was, in fact, John Chapman, a nurseryman, and diligent, painstaking businessman. He did not spread seeds randomly. He carefully selected locations and planted nurseries of apple trees. He built fences to protect them from livestock and other predators. He left them in the care of locals who sold trees on shares. He returned every year or two to check on the nurseries and care for them. He didn't plant trees for their apples; he planted orchards to establish land claims on the frontier: at his death, he owned 1,200 acres of valuable land. (He would return from time to time to some orchards and sell off the orchard and the surrounding land.) In the context of this platform, he was a missionary of the Swedenborgian church toward the end of his life, "quick to preach the Gospel as he traveled," and converted many Native Americans.
The reality of Johnny Appleseed is not a bad model to look at. But the legend should be left behind, as most legends should.
We cite the "one sows, another waters, another reaps" verse - but if no one is doing the watering, weeding, and harvesting, the fruit will be lost. Paul might have been sowing, but he had the expectation, intention, and planning for others to come and harvest. He sends letters, he plans to come and visit, he sends others to check on them. A long-term harvest requires a plan and a network of collaborators who see the harvest all the way from sowing to reaping.
Doing short-term work - flinging seeds randomly - without taking the time to think about, plan for, and implement the long-term as the framework for the short is a short-sighted, lazy effort. By our laziness to think the matter through, we condemn future generations to a life without access to the Gospel and the Kingdom.