We create three shopping campaigns which respond to three different types of search terms. P#0 for high ROI terms, P#1 for low ROI and P#2 for new terms. Our system regularly updates these campaigns, it pushes high ROI to P#0 and low ROI to P#1. If you pause P#1 (low ROI), system will only check P#0 and push relatively low ROI from P#0 to P#1 (which is already paused). Eventually, P#0 is going to end up with very few search terms. Hence, we suggest never pause campaigns.
The alternative is that you bid low for P#1 and P#2 campaigns to optimize your spend. Again, this isn't what we recommend. Our system does reduce the bids as per the data available. It takes time. But you will see results. By altering the campaigns, you are only making it difficult for the system to function.