OMNI
My avatar speaks for itself.
I live in the midst of production for many television programs, and I've done Production Assistant work in the past, and yes, the actors are very busy. When they are not filming a scene, they are often rehearsing, running lines and/or are blocking shots. Rewrites happen all the time, so lines much be relearned. Plus, a scene is rarely shot from only one angle, and that doesn't just mean they have more than one camera on them at a time. They RESHOOT the scene from another angle, and then it's finally edited together to show changes in perspective. That all takes time. That's the reason why you'll often see beverage levels change in a scene when they swap perspectives.
You'll even see them going over their lines (and learning new ones) while they are in the makeup chair.
There is a reason why so many television actors have drivers take them to and from shooting locations. They're often too damned tired to take themselves to and from those locations safely.
as someone who works with doing the REAL grunt work for moveis series shows etc you are not telling me something i dont already know and i still think they have a breeze ie 2-3 weeks of 6 day 14h/day work but then they can relax for quite sometime on the oney they made people like me on the other hand who actually make the stuff look good cut it toghther post production VFX etc work those kind of week/days/hours for almost the whole fricking year as when a 6-8 month project wraps up we cant just take a break for a few months no we have to start on the next 6-8 motnh project right away or most of the time during working on the first project and lemme tell ya een tho some of the senior guys get a decent paycheck overall compared to actors directors and producers we are on a slave labour wage for the sheer amount of work and hours we put in.