I feel like one can expect 6 day weeks to garner more work produced for a few weekends, but after a while that benefit fades into just taking productive hours from one day and moving them to another. My maximum production efficiency with the most usable work produced is 50 hours/week over 5 days, and honestly of that 50 I expect that I'm only REALLY productive for 6-9 hours/day but those productive hours shift from day to day and the 9-10 hrs caters to that.
We don't need just "FX elements" we need "good/final FX elements". In order to create that an artist needs creative energy and mental focus. There's only so much of that you can squeeze out of yourself a day, if you squeeze that extra back up energy it just takes some from tomorrow. Each day it takes some from the next day until you basically come it tired and useless. Unable to crank out final work in a timely manor just be as good as our auto pilot is. Managers often feel better about having artist around for longer/more hours. They feel like if they're in their seats they'll get more work done, and all time in a seat is equal. That misconception is why we work the way we work.
Our goals are the same, produce the best looking work in the fastest way possible. Get shots to final with the least number of hours. For weaker artist, or anal Sups/Directors that's done by producing the most iterations possible so that the notes can clearly define the direction. Iterations need to be done b/c there are things in the shot that are not right. Good artist can give themselves notes and final a shot with minimal iterations, when they have the creative energy and mental focus. This saves time in dailies and across the board and ends up working out for both the artist and the company.
The hard thing, from the companies perspective, is the weaker artist who need more iterations to get their shots to final. In that case the company might feel the need to ask them to do more hours. I get it, but across the board 6 day weeks, seems to be more costly than it's worth for both the artist and the company. I normally reserve the 6th day for the final 2-4 week push.
On this current show, after many 6 day weeks, I feel like I come in and don't have my usual artistic power to make final looking work with ease and crank out whatever is asked of me. I feel drained and artistically weak. I can't think of what to work on next, when I render something I sit and think, lose my train of thought and am comparatively unproductive. My joy in this occupation is cranking out work I'm proud of faster and better than expected.
Only the managers will know what works best for each artist on each show. There's a lot to consider on their part, and that's not my expertise. I only know management of myself. I hope that my perspective is helpful to you on future shows.