What potential issues can arise from not setting the timezone in PHP?

Without setting the timezone in PHP, date and time functions may return incorrect results based on the server's default timezone. This can lead to inconsistencies in date and time calculations, especially when working with time-sensitive data or displaying timestamps to users in different timezones. To solve this issue, it's recommended to set the timezone explicitly using the `date_default_timezone_set()` function with the desired timezone identifier (e.g., 'America/New_York').

date_default_timezone_set('America/New_York');