In my FC at least, people do the FC crafting here and there in their free time, but no one actually forms a group and crafts together at the same time. People mostly just contribute materials and the officers have to assign the projects and take out the finished products.

It ends up just being a hassle to call in 3 other people to stop whatever they are doing just so I can take out the finished product and put up the next project. Sometimes I want to work on projects for a long period of time but I can't because that would require me to ask 3 other people to stand around and do nothing while I throw materials into the thing.

Long story short is, the restriction doesn't do what I think the developers intended it do (have crafters all join up and make things at the same time together), people at least in my FC do the FC crafting by throwing the materials in the FC chest when they can. The light party restriction just keeps us from getting projects done because it's a hassle to make people go out of their way. I could get a lot more projects done without this restriction.