What are the differences between an estate with a Will and an estate without a Will (in relation to the Grant of Representation)?
A "Grant of Representation" is the collective term for a "Grant of Probate" or a "Grant of Letters of Administration".
A Grant of Probate is a Grant given to the executor (or executrix, in case of a female) named in the last Will of the deceased person. Whilst a Grant of Letters of Administration is a Grant given to an administrator who is the next-of-kin (e.g. the deceased's spouse, child or parent, etc.) where there is no Will, or where no executor has been appointed in the Will.
A "Personal Representative" is a general term for either an executor or an administrator. This Personal Representative has the authority to deal with the deceased's estate, such as to manage and distribute the relevant assets to the beneficiaries.