Usualy i develop a somme complex applications, and by my experience, i think that is good to had OOP, but it has a lot of functions do not has a commom purpose, do be a classe !
Imagine that you need functions to these common tasks: normalize strings, get register id, get date and format of the parts, ... !
By other way, i commonly use constants (ex: define("DSN","oci://...")), and global arrays (ex: $months = array(1 => "Jan", 2 => "Fev" ...) )
I usualy create a directory only with configurations: commom constants and arrays
gradually i use more OOP unlike global functions and variables !
Example: the my class in this site for calendar picker :-)
It has so many uses in diferrent contexts and apps ... !
But i think that never do one app can be only OOP !
I had a lot of classes to submit, but i had to mutch busy, but since its posssible i submit then !