I did EC with my DD.
Its not about potty training as such. The way I see it is...
When a baby is born they have a set of instinctive cues which they use to communicate needs. If the need is not met they have crying as a back up to let someone know that something really is up now.
To begin with a baby doesn't know that it is hungry, needs to eliminate, has wind, needs to sleep or anything else. All it knows is that something is not quite right. The baby signals and if the parent responds with something that makes the not right feeling go then the baby learns that the feeling + that cue + parent's response + baby's response = baby feels better.
So if the baby roots, the parent offers milk, the baby takes the milk and the hunger is gone.
The baby doesn't know that it needs to wee or poo, but the body still signals to the brain that there is a need. So if the baby squirms or makes a certain face, the parent offers an opportunity to use a toilet or other appropriate place, the baby wees or poos and the feeling of discomfort is gone.
In both cases the parent and baby are learning from each other. The baby learns that certain cues get the sane responses each time and associate them with certain needs. It doesn't have to be any more difficult than learning any of your new baby's other cues. And just like other needs and wants, as the baby develops the need becomes less urgent and they find more ways of requesting that you meet it.
You don't have to be nappy free at all, or can be for just some of the time. Personally I used nappies alongside EC, but when I have another baby would use nappies less next time round.