Mystery Fabric: Magic or Mayhem?

     I am a thrifty person. That's the nice way of saying cheap! I absolutely hate spending money. When I have to hand over large amounts of money, I take a deep breath and do it quick-- just like ripping off a Band-Aid.

...do you have layaway? can i work the bill off? sell my firstborn?

    I do this quite often in the fabric store. Sewing isn't, after all, the cheapest of hobbies. It requires fabric, thread, zippers, pins, shears, patterns, a sewing machine isn't a bad idea; not to mention all sorts of other little odds and ends a beginner probably wouldn't dream of. Horsehair braid? Hem tape? Bias tape? Twill tape?!  GROMMETS? And holy crap, you're supposed to use different needles for different types of fabric?!
     Buying sewing supplies is a hard process for committed cheapos like myself. BUT.
     I do try. Cheap notions aren't a big deal; bigger things are opportunities to put coupons into action. Sometimes Hancock Fabrics has 99 cent pattern sales. I spring into action I tell you-- limit 10 per customer? I won't leave with under 8. I'm on the email list for Joann's and Hobby Lobby, and every couple of weeks I get a Hancock Fabric booklet with all sorts of lovely sale info and coupons. Sidenote: Hancock Fabrics has the best sale names and they have sales going on pretty much constantly. Seriously, Sassy Saturday Sale? (which I'm pretty sure is every Saturday) How can you beat Sassy Saturday? Anyhoo...
     Pretty much all fabric I buy is on sale/clearance. Scratch that. I never eva buy full priced fabric. In case you haven't inferred, Hancock Fabrics is my go-to sewing store. I don't know if every Hancock Fabrics is the same way, but mine has a bunch of folding tables grouped together with signs calling you to spot the sale or something like that.

 I spot those bolts' socks off. I spot them from a mile away. I spot more bolts than someone watching a lightning storm. I spot them so hard they don't...know....what spotted.....them? OK, the point is, that's where I find my fabric. My cheap, wonderful fabric.
     Now some of that fabric is just ugly, and no one wanted it, so they're trying to get rid of it, duh. Some are just little remnants. Some have little flaws and stains. And some of that fabric is unidentified material that doesn't look half bad, to my eyes or wallet. Attached to the bolt is a note about unknown fiber content, which I'm sure correlates directly to that non-heart attack generating price. I have a bunch of this kind of fabric.
     As far as I can tell, knowing the fabric is important so you know how to take care of it/not burn it while pressing. As far as sticking to fabric suggestions for patterns, I use that for general guidelines of how heavy or stiff it needs to be.

$3 a yard?! the Wizard of Oz has tampered with these prices!

     So for me, mystery fabric is magical, hands down. Magical in that I get it for cheap. But I feel like more experienced sewers/sewistas/peeps who sew would frown on this mentality and say it's more important to have specific information about your material so you can determine if it's right for your project and take proper care of it.
     Is there some vital information I'm missing that makes mystery fabric untouchable? I really don't care too much about knowing exact fiber content anyway; I've seen burn testing mentioned as a way to determine it, but the thought of burning anything (aside from candles or tiki torches) I spent my dinero on kind of makes me cringe.
   The reason I've been pondering this is that I'm using a Mystery Fabric in my next project, Simplicity 1873. Hopefully my dress will be half as cute as Miss FlowingBlondeLocksandEightFeetTallLegs's. But you can bet I won't be wearing it with that little coy half-hint of a smile. Nosiree, I'll be jumping for joy if I can pull this one off.