close a/c's are usually credit cards where the company closed them either by your request or due to inactivity. could also be paid off mortgages or other loans
credit card — it’s what can give you a long credit history so if closed they can shorten your credit history
length of credit history is part of formula for determining credit score
so when an older account (like mortgage or student loan) falls off your report, your score could drop since you’re losing the credit history that comes with that account.