An average person holds 10 loyalty, membership and business cards inside the wallet. When combined with 3-5 credit cards, personal ID's, coins, one to two keys, old receipts and small bills, the wallet turns into one bulky health hazard.
People who have a habit of keeping their bulky wallets in back pockets, unwittingly put a lot of stress on their spine, which turns in a chronic pain after a while.
It makes wallets the real annoyance. Especially during the summer time.