Record Sleeves - Which ones and where?

Sorry for being dim, but what are outer sleeves, why are they important and how do they protect the LP from wear, tear and dust? I've heard of plastic covers used to protect the album cover, but never heard of an outer "sleeve" that could protect the vinyl record itself. Thanks.

Thanks for the tips guys. As far as the outer sleeves(Hartwerger, I believe the "plastic covers" and "outer sleeves" are one in the same, and keep your albums from getting scuffed up), I like the idea of a thicker 6 mil sleeve (thanks Markd51!). I've been looking at the 3 mil, but I've never used any outer sleeves and so I don't know what the quality will be like. Do the outer sleeves fit snugly or are there edges that will fold under when I place the albums on shelves and end up taking away valuable real estate on my shelves with the "bunching up" of the plastic on the bottom?

Hartwerger -
Outer sleeves in my experience are typically larger and heavier gauge plastic "envelopes" that will accomodate the entire LP package...vinyl w/inner sleeve + jacket. I don't have these on all my LPs but where I do my practice using them with inner sleeves is to insert the Lp into the inner sleeve with the open end of the inner sleeve facing up or "North". Slide the inner sleeve into the record jacket (maintainng open end North) and then insert the record jacket open end first into the outer sleeve. The open end of the outer sleeve is at the spine end of the record jacket. The open end of the inner sleeve is pointed at the top of the inside of the record jacket. Dust (to anthropomorphize) trying to get in has to make a few 90 degree turns to get to the vinyl.

Sorry Hartwerger, My post did leave a bit to be explained, and was sort of vague re-reading back.
I'll explain further.

My opinion of Outer Sleeves, is that yes, they will actually protect the LP itself, even though one might not be able to see immediately how this is.

Imagine this if you will, your LPs sitting on a shelf, rack, or wherever 9Hopefully in an upright manner, and as they sit, the dust accumilates. Two weeks, two months, two years, six years, etc. etc. Imagine if you will, the amount of dust landing on your beloved, and expensive LPs. If you live in a desert climate like I do in New Mexico, all the more reason for the Outer Sleeves.

Eventually, dust will get in, thus intruding into the inner Sleeves, and ultimately the LP itself even if you might think it won't. The other obvious benefit, is the protection of the LP Outer covers themselves.

When a person has just perhaps a dozen LPs, then maybe one might feel what's the use?, but when collections start numbering into the multiple 100's, I feel it's very wise to protect this investment as well as possible.

For years I went without, but for the last 10 years I haven't. I feel the Outer Sleeves were a very wise investment, and whenever I buy used LPs, they get the complete treatment, Last, or Disc Doctor Cleaners, Last Preservative, and always new Inner, and Outer Sleeves.
I know when I go to pull one of these LPs, even if it's a year later, all is fine, and spotless. Hope this helps, Mark

I forgot to mention that I hit the motherload during the past week finding well over 200 albums in virtually brand new condition (even the sleeves look like new) and all for $1 each. Everything from obscure Gentile Giant LP's to Ry Cooder, Steely Dan, Dave Mason, Dire Straits, and on and on. I also found a near mint Ariston RD-11S that works perfectly for $200. What do you guys do with all of the original sleeves after you put your albums in new ones? Will they fit in the new outer sleeves along with the album? There's a lot of info on most of the original sleeves that I like to read while I'm listening, and I don't want to have to search through hundreds of original sleeves to find the one I'm listening to.