During your lifetime you may have accumulated a few bits and pieces. Some in the form of investments, savings or pensions. Generally they can be easily valued. However it may be important to understand the value of other chattels. For example you may unknowingly have an item of value that is included in your Will under your general chattels that may have great value. This is good news for the beneficiaries. However it may have unintended consequences whereby you are giving substantially more to some rather than others, simply because you didn't value items during your lifetime.
Generally, in any Will, there is no need to list assets. As an individual you may wish to keep a list of what you own. This can be really useful to your executors. In this digital age you may have investments or bank accounts that are invisible to your executors unless there is some evidence it exists.