Is there Any CONS of making a big common function file in php / or other languages

I just wanted to ask is there any problem or cons if I keep adding new functions to a single file and if I import this function file everwhere. Currently, I am having 280 Functions in functions.php and 5335 Line of codes in functions.php

I am expecting to add more around 500+ functions in the future. Is there any cons in terms of Best practices / Optimization?

My main focus is on optimization.