One of the jobs of an exercise scientist is to formulate the most efficient training program, using the most up-to-date scientific consensus on the evidence. The efficiency of a program can be measured as the degree of adaptations in a set amount of time: the more gains over this set amount of time, the more efficient the training program is.
Another way to measure efficiency is to consider the least amount of work needed to obtain most of the adaptations. This concept of efficiency is most used in clinical settings and less in performance-oriented settings.
The pursuit of the highest degree of adaptations in a fixed time-span is regarded as the maximalist approach to training, while the pursuit of the highest degree of adaptations with the least amount of training is regarded as the minimalist approach.
The maximalist trains as much as necessary to become as strong as possible, or as big as possible, in a limited time-span or as quickly as possible. This is the approach used by strength and physique athletes, and all athletes that need strength and size for their sport.
The minimalist trains just enough for gains and stops right before the point of diminishing returns. Training this way is perfect for those who do not like lifting weights, those with limited time to train, or those who want to get the benefits of strength training but aren't necessarily interested in being the strongest or biggest they could ever be.
Maximalist and minimalist approaches can be used together: some may want to grow one part of the body more than another, or become significantly stronger at one single lift. In these situations, utilizing a maximalist approach on a small set of muscles and a minimalist approach everywhere else is a viable strategy.
The difference between the two efficiencies must be kept in mind when deciding how to plan a training program for ourselves or our trainees. The strength training variables apply to both these approaches, but the way that they are manipulated depends on the objective of the trainee, and in turn on the measure of efficiency that most closely matches the objective.