Objects help encapsulate complexity. For most PHP programming, it's impossible to write good, clean code for any reasonably complicated application. Writing OO PHP helps you put that code into its own box, isolating it from everything else. This has several benefits.
- As long as your object has clearly defined inputs and outputs, the way that the object does what it does doesn't matter at all - storing/retrieving data could go from flat file to XML to memcache to MySQL to Oracle, and you only ever have to concern yourself with one single object.
- As long as your object has clearly defined inputs and outputs, you can completely replace it with another object that has the same inputs/outputs. Decide at runtime whether you want MySQL, Postgres, memcached, or HTTP POST/GET requests to a sketchy server in Indonesia.
- OO makes unit testing easier. If you can define what a specific object should do (i.e what results it should give you for a given input) then you can easily write code to test thousands of values against that code and check the results, and you'll know instantly if something breaks.
- The more of your code you 'hide' in objects, the less of it you have to see when you're using that functionality. I wrote a polling application once in PHP that handled all aspects of polling - database interaction, poll generation, voting, ranking, sorting, and displaying - and I only needed one line of code on my website (
Poll::Display()) to implement the entirety of what the app could do - which made maintaining my homepage far easier.
Keep one thing in mind - OO in PHP (even PHP5) isn't very good OO compared to a language like Python or Ruby. The everything-is-an-object model in Python is what made me OO programming really click for me - and as a former PHP programmer (and doubly-certified Zend engineer), I strongly recommend exploring Python's OO if you want to understand what OO is all about. It will help you write better PHP code, at the very least.
