Wills

Is the point of the will to document all my assets though (ballache!) or just say "take everything I have and let this person decide"?

(Editing to add details)
It’s to decide the ownership and beneficiary rights over your assets upon your passing. Documenting your assets is a job that ultimately falls on the executor, as they’re most often the person to fill out the HMRC tax return quantifying your estate. The level of detail required can vary according to a whole mess of reasons, and the more complex the estate, the more detail will be required.

If you want to and are able to document everything in detail, that’s great and makes things easier, especially if you’re dividing the inheritance. If you ‘leave everything to Mrs. Hippy for her to do as she likes’, it’s still helpful to put that in a written will. If you don’t give specifics somewhere and just say ‘the money in my four UK bank accounts’ then the executor will have the job of tracking those down.

If there are people who might have legal right to an inheritance, like children or exes, that’s when a solicitor’s support can help prevent a lawsuit, or at least make the will much less likely to be overruled by a court.