Would you say there are three main schools of thought on the use of sick leave?

One being, use sick time now, enjoy the sick leave as much as you can while "sick", don't make it up.

The next being, use sick leave when needed, and then pick up trips in MUS to keep adding to the disability account.

And lastly, try not to ever use sick leave, max out the disability account at 686, and put your 72 hours of sick into the 401K every year after that.

Anyone care to comment on why one is preferred over the other? How long after using sick time do we have for MUS?

You have picked an interesting topic to discuss on an open forum.
The short answer is....... call in sick when you are not fit for duty.
As far as using MUS, depending on how much sick bank you have, how often you are ill, and other factors; MUS could be a useful tool to re fill your bank with trips that are very attractive but you otherwise might not be able to pick with other M/U options.
I don't have an answer on how long your MUS bank lasts, my guess is a calendar year.

Then it goes to MUD.

And when you retire, the 686 hours (or whatever you have in the sick bank) goes "POOF". Gone!! I was one of the folks that believed sick leave was for when you were sick, not a scheduling tool when a deadhead didn't work out or I didn't like a trip. I retired with over 600 hours in the bank.

Sorry, but that is just dumb.

No sh1t.. That's a 100 flights the company got for free!

Obviously, when sick or not fit to fly, don't hesitate to call in sick.

When considering how often to call in sick or whether or not one should use MUS/MUD, consider your age and how many years you have for the company to contribute to your 401K. $15,000-$17,000/per year into one's 401K beginning around the age of 50 will compound nicely.

Once you reach 60 or so, consider another strategy to manage your sick bank.

My "strategy" was two fold. Once I hit the magic number, I got the 401(K) deposit for a few years plus I had almost 10 months of sick leave to use if something catastrophic happened to me. Just call in sick and change default bid to highest paying line with carryover. Wife wouldn't have to deal with LTD or any other stuff for quite a while. Between vacation and my sick bank I could draw a full paycheck for well over a year. The last year before retirement I started to draw it down a little bit (but it still bothered me to call in sick when I knew I could probably have gone to work.) What ever works for you is okay with me. Sorry you think I am dumb for doing what I thought was in my best interest and showing a little integrity.

Just make sure that you don't call in sick when it's a family member, not you, that is sick.

I've repeated the story enough times, but I was admonished by my ACP (Don M) for calling in sick when my wife was in labor.

Sick leave is for when YOU'RE sick. So if they call and ask, that's why you called in.

More or that reasonable man "just culture" at FedEx.