When you take the leash off your dog, the only means you have left to control him is your voice. Practicing an exercise off-leash before your dog is ready for it is almost certain to set your training program back a week or two. Even if there appears to be no immediate problems, you will be setting the stage for trouble down the road.
So, how do you know when you are ready to try a particular exercise off-leash? Well, if your dog isn't performing the exercise almost perfectly when you have him on leash and you are only two or three feet away, don't expect him to perform well when he's free and you're ten or twenty feet away.
Similarly, if you have to use the leash to get him to do the exercise when he's on leash, he's not ready for an off-leash attempt. Don't take the leash off until you're sure you won't need it.
Good luck with your training!
Neil