Well on a basic observation. Having a large project loaded into ram may yield less ram for rendering so perhaps a slower render.
But I think the real reason to have multiple projects for various shots is for versioning, and potential errors. I think many of us have had a corrupt project file that won’t open. By separating your work you’re more likely to maintain most of your work if this occurs. Also as for versioning, you can save multiple copies of particular shot as you work and return to a specific state in the process.
Lastly if you are working with multiple artist they can work on specific shots and finish them in one project. Otherwise you would have to update your project with new versions of comps and import massive projects that get bigger and bigger and the next thing you know the project isn’t opening and ahhHHh!