It makes natural sense for the robot to move from identifying spills to cleaning them up. Lots of people say "well somebody just sees a spill and sends a human to clean them up" which doesn't work when the first person to detect the spill is the old lady who slips in it and breaks her hip.
If Marty is roaming the aisles at a reasonable speed (i.e. not so fast as to endanger shoppers!), there's still a substantial chance that the first "person" to detect any given spill is the elderly person with the fragile hip, while Marty ambles around the other side of the store.
So how many robots are needed per store if they're to have more effective coverage than asking the employees who roam the aisles tidying and re-stocking shelves, helping customers find things, fulfilling click-and-collect orders, etc., to also report spills?
Or perhaps these stores don't have any such employees on the floor -- they're just an array of unserviced aisles, with some staff at the checkouts?
>If Marty is roaming the aisles at a reasonable speed (i.e. not so fast as to endanger shoppers!), there's still a substantial chance
Still substantial but less than without it.
Most of the restocking and cleaning happens when the store is closed. Customers don't want to have people getting in their way stocking shelves and you don't want to be mopping floors (other than cleaning up spills) when customers are walking down them.
