I am daily checking my FBS..and once in week when there is holiday and I am at home I do check my PPBS.
However I think you can always cheat PPBS with low carb diet...long wheat diet....or may be eating lunch in small quantity...
You can always cheat PPBS...but for FBS you don't have any sure shot control.....your liver ....brain will release the sugar in your blood....and bring you to diabetic level.
Although it is said if you exhaust Glucagon and glycogen then liver may not have sufficient sugar for release....still liver will convert sugar from other sources and keep sugar level up.
So FBS is right marker to check???