[norhi999]

There is such thing as the bus factor*: he/she can get sick, force-major'ed etc. and that will stall any progress whatsoever, as engineers are people too. Plus can't assign one person to a three different tasks/locations that require attention simultaneously.

*https://en.wikipedia.org/wiki/Bus_factor

[jsiaajdsdaa]

I could see having three engineers working on three totally separate projects, but three on the same project usually makes things slower.