You probably show it to the immigration officer. Later maybe to a customs officer if you have goods to declare or they pick you out for customs checks. Customs is about goods. Immigration is about persons.
A acquaintance of me get denied entry yesterday comming back from Ireland after being there 3 weeks and before he stayed less then 90 days in Thailand on a 60 days exempt plus extension.
Maximizing your stay with back to back entries will eventually fail. Recently more people got denied entry even after just one stay.