Taken from:
http://www.ni.com/white-paper/5423/en
"Polling vs. Interrupts
A key consideration when designing a LabVIEW real-time application is whether the system needs to concurrently perform its time-critical function along with other non-time-critical operations, such as local disk logging or communication with the host. This decision dictates the basic architecture of the real-time application.
Polling can be used for I/O mode in the case where the system has no non-time-critical responsibilities, or, more realistically, the system uses a state machine to schedule time-critical and non-time-critical tasks to operate sequentially. For most I/O drivers, polling mode is faster than interrupt mode.
Although slower than polling mode, interrupt mode is the more common for real-time applications as most applications contain a mix of time-critical and non-time-critical functions occurring simultaneously. Interrupts allow the I/O portion of a diagram to suspend its operation and allow other code, such as communication and logging, to run while the hardware is in the process of acquiring data. Once the hardware has finished its acquisition, it raises an interrupt to notify the software that it should resume with it’s time-critical I/O processing.
As noted in the table, we ran the single-point tests using the appropriate I/O mode to highlight the differences between these two modes of operation."