1. When i find it somewhere on the floor under furniture, too dusty to use or give away.

2. When it’s gotten on my last nerve just looking at it.

I do throw away some fabrics of usable size if the fabric is so thin that you can see thru it. That is not fair to the person you are giving it to or selling it on line or at a garage sale. I have had fabrics given to me that are just not good for anything except the trash.

Rob's aunt used to love getting garage sale sacks for me, which was very kind.
But if it was permeated with cigar or cigarette smoke, you know the kind, greasy yellow, into the burn barrel it went.
The same with musty/mouldy fabric. It is dangerous to be around, and not worth health to try to bring back to useability.

I haven't had any cross my cutting table for years, but I've never kept poly and poly cottons. I don't like the feel and once stained seemed impossible to clean when I used to wear it all the time.

Time and place for everything I guess. That said, I cut fabric down to 1.5" squares and have used thousands and thousands of them...bring 'em on ;)
Good question Bearisgray, usable is different to all of us!

I will save scraps for awhile and then I start feeling like I should do something with them. When the scraps start sending me guilt vibes. Out they go at any size.

I would never throw any fabric larger than an inch in the trash. If I don't want to use I would donate it. Someone would be thrilled to get it.

Since my quilts are baby and kid donation quilts that probably be tossed away when the baby outgrows it, I am not fussy about using poly-cotton fabric, or poly batting, but I donated a lot of too-thin stuff back to the thrift shop. And, I have to admit to throwing out scraps smaller than 2"x2".

Red bleeders. Smaller than 2.5" square. Strips narrower than 3/4". Thin/loose weave fabrics. Ugly/lost appeal yardage gets donated to guild grab table.

I laughed reading this but I'm the same way. Sometimes I get tired of a fabric and try to put in a bag for the thrift store or just toss it in the trash.

Fabric covered clothesline baskets are my new use for otherwise unsuitable fabrics. Carol Ann Wilbourne spoke at our Guild recently and taught a workshop on making them. Yesterday I started my second basket— this one using a great dark blue that I couldn’t get to stop bleeding. Since I don’t expect a basket to be washed I think it will be put to good use this way. It is really just color you see so an unsuitable print would be great too. Carol Ann painted some with Shiva Paintstiks when she was disappointed with the color, so even bad color might not be unusable. They were fun to make and popular enough that each month our members bring a few more baskets for Show and Tell. The results have been beautiful, useful, and easy to construct. You might search for fabric covered clothesline baskets to see examples and tutorials.

I pretty much only throw away trimmings, strips less than 1" wide, odd-shaped bits that are too wonky to be useful to me, and lousy-quality fabric that I know I'll never use. Very occasionally I'll throw away fabric that's particularly hideous-looking, but I do try to find a use for it first. (I really hate throwing anything away!)

I pass narrow strips, selvages, and crumbs on to someone else, as I usually don't have the time (or patience) to work with them.

Anything I can get a 2-1/2" square out of, I keep for my own use or save for swaps. :)