Of course, then my thoughts turned to Software and then in some weird connection I jumped into the Man Month Myth, renamed the Person Month to be more gender neutral, and it occurred to me that yes it still happens and yes in some circumstance it may work. Though those are slight, and slim. It of course depends.
Let's look at some examples:
Street Cleaners: the more the merrier! It doesn't take much domain knowledge to pick up trash on a street, or rake leaves from a yard. All you need is some coordination and a slight understanding of tools. Of course, coordination with those tools will make the job faster, a group of 4 or 5 teens could do well, if those are the only resources we have available. It's like after a party at a house, or a bbq, the more people taking little tasks and doing them, the quicker the whole task get's done. I don't want to be demeaning but at it's core there is not a lot of skill involved in cleaning up, using a broom is fairly simple as is carrying a bag to put trash in - at this point the main skill is knowing what is trash. So at this point the skill level is not high, and the tool usage ability is low.
Too many cooks spoil the soup: yes, that adage does have some relevance. The reason you want one cook is because he understands how this dish should taste, everyone is slightly different and the more you have the more additions you get until the soup is a mess. Also, hardly tasty. Not everyone has the same taste or background to know what a particular dish should be, the best restaurants do well because every dish they have has consistency but this is due to long hours of training and knowledge transfer. So we have a medium skill level and a tool usage ability is getting higher, but now we have an added knowledge transfer quotient to add in as there is a lot to know about making good soup.
Software: it depends on the domain knowledge and skill set. The high up the domain tree you go the more it requires a specific fit. Sure you could add one or two more Engineers to your project BUT those Engineers had better be really familiar with the project, specs, and domain or you do more harm than good. The specs have been discussed, meetings have been held to discuss code and flow and design, there may be a lot of documents, depending on your environment but there is also a lot of knowledge transfer. There is a high skill level, a high usage requirement for tools and a lot of knowledge transfer.
So, can you add more people and get more done? Yes, but only in specific situations. If people have the skills, tool and domain knowledge then adding them in is not an impediment, but this is rarely the case. Although if you have an environment with lots of switching between teams then some of this may be in place but you have to know. If you don't analyze the situation first you will just make a mess of it. Like the soup.