Adding Avatar to profile via URL link - insanity or genious?

[#1]

Ok - can someone pls explain to my slow brain why it is in just about every online forum that invites you to have a photo (avatar) in your profile, the suggested process is to grab your photo which you have had already to place on another website, i.e. you have to paste a URL into the Avatar upload to get a photo which you placed elsewhere!
For some reason I get an irrational anger when I even try to work out why this convoluted process was dreamt up. I mean - its like going to the local Supermarket to buy your shopping then actually ordering it online from a computer in the Supermarket rather than picking the food off the shelves. Its daft! Well at least, without me knowing the benefits it seems ridiculous.
No doubt there is some genius behind this weird process - please can someone explain step by step why this convoluted process exists and what it sets out to achieve over and above simply uploading a picture from your PC directly? 
Thanks

[#2]

From the profile page:
You can change your personal information on this page. This information will be displayed throughout Forum. If you aren't comfortable with sharing some information, simply skip it - nothing here is required.
* I have my own pic:
Specify your own avatar by URL. (ex: http://www.mypage.com/mypic.gif)
* I will upload my own picture:
Choose the options marked * and use the Browse option to navigate to the location of the pic you want to upload, then Robert's your father's brother...

[#3]

One plus for having the avatar as a link is that the forum won't need as much space on the server, hence will be cheaper to run.
A million users each having a profile avatar @ around ~1MB in size, what does that equal in data space? Well, even numbers in thousands of users is still a lot of space.

[#4]

Quote from: Jaggies

From the profile page: You can change your personal information on this page. This information will be displayed throughout Forum. If you aren't comfortable with sharing some information, simply skip it - nothing here is required. * I have my own pic: Specify your own avatar by URL. (ex: http://www.mypage.com/mypic.gif) * I will upload my own picture: Choose the options marked * and use the Browse option to navigate to the location of the pic you want to upload, then Robert's your father's brother...

Thanks for your reply. Pls can you explain why forums like this invite people to point to a personal picture using a URL? This is the one thing that is driving me mad because I dont understand why that process exists for anyone. I get the part about 'personal choice' about what one shows - for me thats not whats troubling me.
Why point to your picture using a URL? I dont get it!!!

[#5]

Forums use html to display the page.  When you want to include an image, you are using an <img> tag.  You refer to the image with a url, just like you'd request a webpage.  This means that if you have an image already hosted somewhere on the internet, you can just provide the url to it and the web browser will load it.
This means you can also do clever things like change the image yourself without having to change the image on the forun you've used it as an avatar.  This also means the forum provider doesn't need to have space set aside on their server for the images.
That make any sense?

[#6]

Thanks Kelly for explaining. I have asked the same question on two other Forums and you are the only one who has actually been able to explain it. The respondents on other Forums just told me to accept that it works, and so naturally I didn't accept it without a rational explanation.
I think I understand most of what you are saying (para two is clear) but my lack knowing what Tags means  that  I don't really get that bit but  I have enough understanding to know now there is a dual advantage to loading images this way now.
Before this explanation I was ready to condemn the whole worlds website authors as a secret society who were born with nerdy habits that meant everything they touched must be unnecessarily convoluted and mystical - but now I see I was being a little hasty making that assumption and judgment!. 
Only joking of course...... I meant half the world!
Only joking.
Thanks for explaining the mystery - appreciated.

[#7]

the tags stuff is the code that browsers read to display a page:
<html>
<head><title>This is the title</title></head>
<body>
This is some text
< img src="http://community.plus.net/forum/Themes/plusnet-brand-refresh/images/header/pn_logo_lockup.png" >
</body>
</head>
This is the html markup which a browser interprets to display a page.  the <html> and </html tells it that it is a html page and to treat everything within as html..  <head> and </head> indicate everything within is the header information for that page.  Between <title></title> is the text the browse uses to put the title window of the page.
<body></body> contains the bulk of the page, in this example just some text and an image.  The <img> is an image, with the src bit telling the browser where to load the image.  If you copy the src but (not including the " and " and paste it in your browers url bar, you'll see that it loads the pn logo.
That is how html tags work.  You can see a much more complicated example by right clicking on the page and selecting "view source" or similar from the menu!   This is the html for the forum page you are reading!

[#8]

For a little insight into the 'black art' of HTML coding I'd recommend having a read here: http://www.htmldog.com/