From time to time it is useful to send documents by recorded or special delivery.
There are normally two reasons to do this: dodgy opponents and important or urgent deliveries.
From time to time you will deal with opponents who appear to be either dishonest or simply totally disorganised. In these cases it is useful to have some independent confirmation that what you have sent has been received.
You will also deal with important or urgent deliveries. Sometimes you will have original documents that cannot be replaced, and sometimes something will need to arrive quickly. Special delivery, or even a courier, can be useful.
There is no reason, however, to send all letters in legal proceedings by recorded or special delivery. This is expensive, and normally has no real advantage. If you are need to be sure that something has arrived the cheapest and easiest solution is to give the receiver a quick call a couple of days after you send it.
Bear in mind that recorded / special delivery can actually slow post down. Items will not be delivered unless they are signed for. If the receiver is out, it can be some time before he arranges for re-delivery or collects the post. The risk of this happening will vary depending on who you are sending things to. A local authority is unlikely to be out when post arrives, but a small businessman may well be.