Is it necessary to use PLUSes in an msXML call instead of spaces?

[MLH]

In the following code snippet, notice
("PIN=1234567890&MSSG=Here+is+a+short+message+-+no+spaces+-+just+plusses&Q1=0")
I have it that way because I thought PLUSes were required and that
spaces would not work. But I have tried
("PIN=1234567890&MSSG=Here is a short message - no spaces - just
plusses&Q1=0")
and the msXML.Send call works perfectly. Does anyone know how or
why the PLUSes came to be used in the first place?
Private Sub Command6_Click()
380 Dim msXML As Object, strPageContent As String, MyURL As
String
390 Set msXML = CreateObject("Microsoft.XMLHTTP")
400 MyURL = "http://www.Arch.com/cgi-bin/wwwpage.exe"
410 msXML.Open "POST", MyURL, False
420 msXML.setRequestHeader "Content-Type",
"application/x-www-form-urlencoded"
'430 msXML.Send ("PIN=8002504133&MSSG=" & GlobalString &
"&Q1=0")
430 msXML.Send
("PIN=1234567890&MSSG=Here+is+a+short+message+-+no+spaces+-+just+plusses&Q1=0")
440 strPageContent = msXML.ResponseText
450 Debug.Print strPageContent
460 If InStr(1, strPageContent, "Page Sent") Then
'470 GlobalString = "Page to " &
DLookup("[TowCoOwnerName]", "qryAdminList") & " successful. If owner
does not wish to be notified. "
470 GlobalString = "Page to Michael Lee Theofilo Andreas
Harvell successful. If owner does not wish to be notified when new
vehicles "
480 GlobalString = GlobalString & "are entered, you may
change this setting in the User Setup And Configuration Screen."
490 MsgBox GlobalString, vbInformation, "Notification Of
Vehicle Entry - " & MyApp$ & ", rev. " & MY_VERSION$
500 End If

End Sub