They put them on to show the brands and logos they support without caring about what they put on the surface.
 
I don't affix anything on mine.

Personally the only stickers i put on my case are the actual case badges. For me it helps other people figure out/get an idea of what is in my rig without having to ask.
 
Example:
Extreme processor,  ASUS motherboard, evga graphics cards, corsair SSD and Memory, and my computer WAS up to date on mod rigs.
 

 
Other than case badges, i could never put any actual STICKERS on my machine. I dont think it looks clean.

Oh definitely, Alacran...heh..I've stripped the stickers off my work PC (Dell) because I hate how it looks with them on....it's all personal taste
 

I usually place about 3 on mine. No more than 4, just depending on how case looks.
 
Usually I slap on my Intel badge, Corsair (PSU), G.SKILL (If I'm using their memory at the time), and then my ModsRigs case badge.

transdogmifier

seabigbear

I only have the EVGA one on mine!

The Bear on top makes it c'est magnifique!

Thank you & there from Billy the Kid!

I personally just can't do it, would remind me too much of a rice rocket.

I never put stickers on my case but i did for the first time like a week ago. So far i dont like it but have been to lazy to peel them off. lol

I have the processor and evga case badge and because the light by the ram slots on my motherboard would bother me at night so I stuck a razer logo sticker there.  Now at night I have a batman like razer logo on my bedroom wall.

I've lost most of mine, too bad because I buy high end stuff. 
 
I can't bring myself to stick things to my case.  it takes away from the case.  If the 1200 had a little spot for em, great, but I'm not losing airflow to be an advertisement. 

stickers?
Case Badges ..show pride of equipment used inside case and pay respect.

BioHazardSperm

stickers?
Case Badges ..show pride of equipment used inside case and pay respect.

Where did you get the ARMY badge?

I personally only put them on if I see them as relevant to me...whether that is that I deem it cool or really like the company or etc. I have a EVGA badge on mine because I like evga a lot (Although I am really really disappointed with the lack of bios support lately regardless of my board and setup being fine as is...its just evga and their image of support being ruined that makes me mad) and I also have a steelseries badge because I see how important they are to professional gaming and such, plus I really love the mouse pad I got from them. I have a razer logo on my desk because that thing just looks awesome...The only bar I put on this is putting the badges on the window of the case...I don't want to obscure the view of the parts.

Ebay actually is where i got the Army badge ,was going to get all of the armed services later ,but got distracted.He may still be selling them it was about 2 1/2 years ago .

A couple on the rear of the case to remind me of what I spent my money on