When should you set up a database connection pool?

hey every1 ive been thinkin bout db connection management lately. weve all seen apps slow down bc theyre busy openin and closin db connections for every single request. so whens the sweet spot for introducin a connection pool. is it when we anticipate a certain num of concurrent users, or maybe when we start seein connection errors. whats ur go-to indicators that its time to implement poolin