Foundation deposits have been found in abundance at Deir el Bahri. Essentially each one is a little time- capsule, buried in the foundations at key points during the various phases of building.
What they tell us about Deir el Bahri is very important. I cannot say for sure why foundation deposits were deemed necessary, unless looking into the future and the assurance that people would know who was responsible for the commission and building of such a temple.
The example above, from the British Museum is just one of many objects retrieved from Deir el Bahri. It shows a well carved cartouche on a stone, which are aptly called "name stones". The cartouche - Maat Ka Ra is the throne name of Hatshepsut. Unclear, but present on the left hand side of the stone is an inscription which names "Senenmut, Overseer of the Works"
Such information can suggest that the location of this deposit was part of Hatshepsut's own work, under the watchful eye of her most trusted "friend" Senenmut.
From this we can get an idea of when this part of the temple was built (in the lifetimes of both Hatshepsut and Senenmut). Such information would immediately rule out her predecessors and previous Pharaohs when considering who is responsible for the various stages of the development of Hatshepsut's great mortuary temple, "Djeser Djeseru" (Holy of Holy's).
This is only one example of the information we can gain from such artifacts.
Other types of deposits i have seen include: Model tools, scarabs, plaques, baskets and more.
Please visit the following site for more information on foundation deposits and also a reconstruction of a Deir el Bahri foundation deposit: