Multiple instruction strategies help students retain what they learn. When multiple instruction strategies are used, students see the subject from different angles, which naturally increases transfer and retention. If, for example, you use both aural strategies (music tapes) and visual strategies (sheet music) to teach music, your students will be more likely to pick up the material, because learning to associate the sound with the notes will increase their familiarity with the music.
Some topics are naturally better addressed with one set of instructional strategies than another. For example, if you are teaching math, it is best to avoid using physical/kinesthetic instructional strategies, because they are not relevant to the subject. Accordingly, some topics naturally demand that you use multiple instruction strategies. For example, electronic music is best taught using a combination of aural and technological strategies, because in order to perform electronic music, you must understand how music and technology work.
Different students have different learning styles. According to psychologist David Kolb, the four learning styles are: active experimentation; concrete expression; reflective observation; and abstract conceptualization. If you use multiple instructional strategies, you will connect with students who would not benefit from an instructional strategy that appeals to a learning style they haven't developed. For example, if you teach science using experimentation, textbook learning, lectures and brainstorming sessions, you will appeal to students who learn through all four learning styles. If you use just one strategy, your lessons will appeal to just one type of student.
Thinking that follows a set, rigid pattern is generally less effective than thinking that is free and original. If you use multiple instruction strategies, you will encourage your students to think for themselves, because you will be showing them there is not just one "right way" of approaching the subject. This won't guarantee that your students will start being creative overnight, but it will help.