Project math really follows its own rules. You don’t get linear benefits from adding to the number of people on a project. Sometimes it seems like throwing four people at a project makes the project span 4 months, when a single person could have completed the work in a couple of weeks.
My son clearly has a better grasp on the real world than his teacher does. pic.twitter.com/S74YL91yjN
— Carl T. Bergstrom (@CT_Bergstrom) December 17, 2016
Yes, if you have one thousand letters to write, and each worker can write their own letters, this works. That sort of thing might linearly scale.
But on most projects, your communication lines are O(n^2) (actually, (n^2-n)/2)… 2 -> 1, 3 -> 3, 4 -> 6. If you’re not doing mostly independent pieces, you’re creating an unofficial management position for every 2-3 people you sign up. Realistically, 6 would be 15 units and 12 would be 66 units, so a mere doubling in time is really optimistic unless the 6 extra workers are making sure that project managers and customers don’t bug the workers actually building the car.
Worse still, usually, the extra 6 workers will need to be brought up to speed mid-project by the other 6 workers on top of introducing the extra ongoing communication complexity.
In other words, (ノಠ益ಠ)ノ彡┻━┻