My team drives on a light touch to the lines, I mostly work them off of voice, with a slight touch to the lines if were doing something in the general public to reenforce what I asked them to do. Here is a photo of one of the wagon rides we provided at a friends farm day tour...
We at one time had buxton bits on the team harness but after getting the bottom of the bit stuck on a snap on my pole, not wanting them anyway as they are primarily used for the wheel horses, we switched over to military snaffle bits. I have light hands on my lines and don't need a heavy bit or one that has a lot of stopping power.
The work harness has simple snaffles. I have plowed with them, driven and again, they are well trained so a light touch and a command, our team will stop. We work with them a lot and we use to do a lot of public events and educational talks so for us, it was very important that they were, and also for the general public. Here I am ground driving my mare Smoke in a snaffle, were pulling a log through an obstacle and yes, I do rely a lot on voice when I did this:
And yes, slapping your lines onto your horses back/rump is very frowned upon. I have done it a time or two but never made it a habit, rather voice or a touch with the driving whip is enough. I have seen people slap the lines often and to me it looks bad.