While we'd probably like to think all trainers are equally adept at using all training methods, that's not true. Trainers all have strengths and weaknesses, so deciding what methods to use should take into account what the trainer is good at and what he or she is not good at. Forcing a trainer to do something he or she is not skilled at is not going to work.
Different training strategies are more and less efficient in terms of time usage. For example, one can "cover" a lot of material by simply telling people things, but while this is a quicker approach it may result in less learning. Small group work typically takes considerable amounts of time. Choosing the right method requires taking into account the time available, since choosing instructional methods that cannot reasonably be executed properly in the time available is a poor strategy.
Balancing of Various Methods To Suit Learner Differences
While trying to match training methods to learner learning styles is, by and large, a pointless exercise based on myth, it does make some minimal sense to include a number of different learning activities so that learner differences can be taken into consideration. However, there's a stronger reason to vary instructional methods in any one seminar (see below).
Ensuring Adequate Variety
Any instructional method or learning activity, if used too often with a group, will start to become boring. We're all experienced with boring lectures that go on and on. However, we often don't consider that something like small group work, or brainstorming will also become boring if it's the only method used. Instructional variety is critical in building and maintaining learner attention.