Once you start reading with AI Read, even when this VI is done executing, the data will continue to be acquired. Eventually you will get buffer overflow error if you don't read this data.
With DAQmx, you can call DAQmx Stop, to stop the acquisition for sosme time. Then you can just call DAQmx Start again on the same task, and continue acquiring. DAQmx Stop doesn't clear the task, so you can reuse it again.
With the traditional DAQ you don't have this option. When you call AI Clear, it will destroy the reference to the channel and you have to create it again to start the acquisition.
Zvezdana S.