The "homework" model in collaborative projects is sometimes necessary, but often inefficient. This default means that we meet to discuss and make decisions, then assign "homework" based on that discussion and make a meeting to review the work and make a further plan. The time increments of these meetings are usually 60 minutes, with the additional email overhead for scheduling. Given the amount of time I and the collaborators will actually spend on the homework the ratio of actual work time to meetings is sometimes not much better than 2:1 if there are many decisions to be made on a project – as in design, analytic, and writeup stages.* Of course if an individual has to do data collection or other time-consuming tasks between meetings, this model doesn't hold!
The products of co-work are often stronger than drafts that come out of independent work. When we program or write by ourselves we sometimes let bad sentences (or copy&pasted code slide by) – I certainly do this. In contrast, when I'm working together with someone I'm more conscious of trying to work carefully and write clearly. And as a supervisor, I like that this model allows us to discuss the strengths and weaknesses of something that we've jointly produced – rather than the model of having me provide a critique of the student's independent work.
Co-working isn't always appropriate. If the amount to be done is too great, or the workload is not distributed evenly between collaborators (whether because of seniority, time, or skill) then it's not the right choice. But for doing the conceptually challenging bits of projects – say, coding the key data analysis or writing the intro or general discussion – co-working can be both an efficient way to get something done and a great way to learn and think together.****
* I also find that for me, given other academic constraints, "homework" often means "comes out of family time" (evenings and weekends).
** Sometimes we work on different parts of the project, but in the same place, so that if questions come up we can interrupt and discuss.
*** Of course, I recognize that this model presumes that supervisors have the time to co-work with trainees; sometimes making this time can be a hard ask. But "can you show me how you'd approach that task" is a often a reasonable question to pose to a supervisor! And of course this model also works as well – maybe even better – with collaborations between two people at the same career stage.
**** In some sense it's amazing I'm writing a blogpost about academics sitting in one place and working together, but that's really the culture we've got - almost every work situation I've been in has involved meetings for decision-making then independent "homework" for the collaborators or the trainee.