The subject of how or why language developed, and whether it was a primarily hardware or cultural advance, is hotly debated. However, given the capability, the individual's and society's knowledge horizons expand considerably. Now the individual can learn not just from direct contact with other individuals and groups, but also from narratives brought orally from afar. The use of language depends on an advance in conceptual abilities, and also provides a medium for promoting such advances. So doubtless early going was slow as conceptual abilities and the richness of the speech medium slowly racheted up over generations.
External storage has several qualities of interest.
It provides long term storage, for retrieval at a later date. It can be used to communicate to other individuals. It is not clear how much thinking skills were helped by early drawing, or how much knowledge was conveyed. Communicating via pictures is potentially powerful, but would have been laborious with early materials, and not very portable. However, it seems likely that early drawing, combined with the communications abilities refined through use of speech, must have played a role in the development of early pictorial written languages.