Square plate tamper is great for getting a solid base and it is good for packing stuff that is too wet or too dry to use a shovel on. If the dirt sticks to the tamper it becomes useless though so I cover the dirt with a blanket or cloth painters tarp. I don't know if I'd say it is easier or faster but you can put a lot more force down to get a really solid base using less water then just finish it with a shovel.
There is one guy who used to be my neighbor and has been building a lot longer than me (I started 4 years ago). He only uses a spade (round shovel) and never uses water. It's like he made a deal with the devil to make perfect lips, I'll see him with a little pile of dry dirt then I go work on something else and when I come back there's a huge jump that's super smooth with a perfect transition. One day I was fixing a berm that was all tore up, so I went down to the creek and filled up my watering can. When I came back he looked at me like I was crazy and said: "what's up with all the water." Even though I know pretty much every digger would be using water in that situation, I felt super small that day. I think he gets more pressure because the force is concentrated in the center of the round shovel then he just hits it until it is perfectly flat. But again I don't think it is really faster and definitely not easier.