I have had a limited run in production sound (working on set) but have almost always been in the post-production seat or team of those projects. This has taught me the tradeoff in time it takes to get the sound on-site correct (or as good as it can be) vs. the amount of time to fix in post-production.
The understanding is that on large productions, doing another take of a particularly large set-up means that much more time to pay the talent, camera department, support teams, craft, the location and also push back whatever is next on the shooting schedule, and that time x all those people and costs adds up fast. Directors (good directors) often check with big-"s" Sound if they got what they needed and then weigh the possibility of recreating the best take with the best sound against hoping it can be repaired in post-production, either with edits from other takes, angles or looped in new recording. Having a budget helps, even if it is frustrating for the sound editor to receive all this beautifully shot and executed footage with completely unusable soundtracks. That's business.
The harder part in my experience is working with small, independent teams. All students of film/video production today are well aware of the power of modern digital audio tools: noise reduction, compositing, waveform repair tools, ADR and the like. So much is possible. The issue is that none of these ever truly replicate the natural, spontaneous performance of the real time and place of the choice take on location. Noise reduction eliminates harmonics and whole frequency bands. ADR sounds too dry, and lip synch is hard to teach. Recreating room tone and reverb is a craft all its own. It can will take hours to renovate the sound track of a simple shot that could have been reattempted in 3 minutes, or that would be fine if someone can just unplugged the fridge in the room or turned the damned A/C off! The final product never meets my standard.
I was introduced to a term when I worked on set of my first feature: "Polishing the turd." The Film school students who worked on it as well taught me that as a turn on the old adage: "Garbage in; garbage out." Basically the latter phrase still holds true, but the fact is: What are you going to do: Make a silent film?
The scariest part for me of all has been that after years of editing sound to picture I've become more sensitive to picking out overdubs and audio errors in big budget film and TV but when I watch the with friends and loved ones and point the problems out, they don't notice a thing. So perhaps, in the end, it really isn't a big deal.
But that doesn't mean that I'm not still going to insist on turning off the A/C in the middle of a summer's day.