It could expose some small cost-cutting opportunities, but in general I wonder why I would want to see all my transactions grouped per merchant/service provider as a consumer. A transaction overview is not something that invites a specific action (as opposed to an sms conversation).
My primary use case now for the overview is to go back in time to see how much I spent on a certain transaction (because I want to split a bill) and this idea would make that process very intransparent.
The core strength of bunq is that my budgeting is done via the different ibans, so I don't really need the transactions overview anymore for budgeting/cost-cutting purposes, since I will find out via the different budgets if I am overspending. In case I would want to cut costs I will need more details which the grouped view will not give me anyway (receipts listing what I actually purchased, so I can take action on it).
'Actions' (and lack thereof) is the key word in this discussion I think.
off-topic: what would help me budget in a better way is if the app would provide a D-day guestimate of when my budget will be depleted based on past expenditure patterns. That feaure would bring me immense value as it would allow me to adjust my spending immediately, so that this date occurs after pay day.