With tires wider than 'performance road' tires (>28mm) then a squeeze with the thumb can tell you what you need to know. If you have 25mm or 23 mm or smaller tires and need to keep them pumped up to 90 or 100 psi, well 70psi feels a lot like 90psi to the thumb, so it is prudent to regularly connect your pump to be sure.
The drawback to regularly pumping your tires is that every time you pull the pump off the valve stem, you put a bit of stress on it and increase the risk of a failure at the valve.