Fair question. The main reason is that I have a small number of clashes with global shortcuts created elsewhere using other software.
I can sort the spreadsheet list on 'Keys' and see very easily where the clashes are. I can then see easily which keys are unused in Vivaldi. I can record any changes that I make a further column.The second reason is that I want to add some keys, and I want a record of the changes and easy access to that record. Again, sorting on keys and recording the added key in a further column is really useful.
In Excel, these changes and warnings can be also be marked using colours as well as further columns.