NPs are generally ASICs so it depends on how flexible the code needs to be that is being executed. If it gets outside of the parameters of what the ASICs can handle it can severely limit performance.

An interesting side effect is a lot of the time the tools running on the main CPU don't have visibility into what is happening on the ASICs as the code doesn't have hooks into the data path at all- it compiles the code and sends it down but it doesn't participate much after it starts executing.