Why use Join-Path - PowerShell

So here's a question I don't understand, why use Join-Path?  I see it all over the place, and it's heavily used by top competitors in the scripting games.  I also see people like Don Jones using the heck out of it.

What's the difference in using join-path vs. just connecting a string?

# is this somehow, better/bore reliable/more aesthetically pleasing

$path = "c:\reports"
$newpath = Join-path -path $path -childpath "$env:computername.html"

# Than this

$path = "c:\reports"
$newpath = "$path\$env:computername.html"

Hope that helps! Jason