Permaculture is about designing sustainable human environments. By gradually moving from an annual to a perennial system, the process becomes more self-sustaining. Annuals will produce more and faster, but the input required for growing is higher than for perennials.
The soil needs to be prepared and fertile, and the seeds need to be put at the right time; then enough moisture is needed for germination and the growth of healthy seedlings. Often, some thinning is needed and either mulch or compost added again before the harvest. Water is essential for most annuals. Then you have to collect the seeds (and some annuals need isolation to prevent cross-pollination), otherwise you have to go out and buy more seeds. So growing with annuals is a high-input/high-output system that can be used at the early stage of development of the design.