[i]concur, those braces are extraneous and accomplish nothing except give people the false impression that only those commands in between the braces are tied to the selected connection.

scon 1
; commands here apply to con 1
scon 2 {
  ; this command applies to con 2
  ; so does this
}
; but this command also applies to con 2, it doesn't revert back to con 1.

this happens because the '{' and '}' are simply ignored by mIRC, and '/scon 2', as we know, switches the connection to 2 for the rest of the running process.

adding unnecessary braces can sometimes improve readability though, here's an example:

goto %var {
  :my

  :labels

  :here
}

; rest of code

the indentation created by those braces allows a person to easily see the extent of the scripter's goto labels.