Salt is an ingredient in almost every pickling recipe we use, whether it's added by the spoonful or making the brine other ingredients are soaked in. Iodized salt is bad but the rest is salt- the purpose of salt is to inhibit the growth of unwanted bacteria and other putrefactants before the fermentation process we're setting up can kick in. Lacto-fermentation takes a day or two to get started, depending on temperature, so the salt guards the door until the lactobacilli are up to the task.
If you're just getting started with fermenting, you might think that the salt will inhibit the growth of the little critters you're trying to cultivate. Seems reasonable only until you see how few pickling or fermenting recipes DON'T use salt. Or until you open something you were looking forward to sampling, only to be warned away by its smell (see the previous post). For instance, beet kvass, as explained by S. Fallon, only has three ingredients: beets, whey, and salt. Well, water, too. Kvass only takes three days to ferment, doesn't seem like much time for other bacteria to move in an set up housekeeping. And folks have complained about the saltiness of previous batches of kvass. We found out the hard way how important the salt is- the salt-light batch wound up slaking the thirst of the compost pile!
Many ingredient lists don't include salt explicitly but do call for a step of soaking the veggies to be pickled in brine- that's salt water. This step also makes sure that your veggies don't get too dry, such as when we had the problem with with floaters.
If you're making a batch of pickles without using an inoculant such as an existing strain of culture, whey (the living, liquid component of yoghurt), or unpasteurized vinegar, the salt is even more important. Root vegetables already have living bacteria in them from the soil they were grown in and can begin fermenting on their own if the conditions are right. This takes a bit longer to start than with an inoculant, so the salt is crucial in keeping bad bacteria at bay. We always use some sort of inoculant as a starter but we've learned to keep the salt in there, first. There's just too much heartbreak involved in having to dump a batch that you've put money, effort, and anticipation time into. And that doesn't even begin to cover the gastro-intestinal grief that comes with eating food gone bad!