With any codebase there are set of conventions that should be followed For example, CONTANTS_SHOULD_BE_UPPER_CASE, functionsShouldBeCamelCase, _private_variables_should_be_underscored, spaces not tabs, etc. Making the decision early on as to what conventions to follow will give you a consistent codebase. The big benefit, though it's more than just aesthetic appeal. There are real, solid benefits to having consistent conventions in a project.
Reading, as a mental process is really hard for your eyes - the human eye can only focus on a very small portion of it's entire field of view to actually read the individual words in a line of text, however we are able to pick up a lot more information than just the small piece we're focusing on. By giving your entire codebase a constant structure, your giving you're brain a distinct advantage in understanding what's going on in the code in front of you. Similar to syntax highlighting (find me one programmer who isn't a fan) giving your overworked brain additional cues can lead to significant advantages in scanning over code to find bugs and make changes. Two of my favorite languages take this one step further. Ruby (and Rails specifically) pretty much defines one standard set of conventions to use through out your code - classes are UpperCase, methods_are_underscored, etc. Python makes indentation (one of the oldest visual cues programmer use to structure code) a feature of the language - ensuring a consistent usage across all python code.
The flip side is also true: code that has no consistent structure or conventions is much harder to grok at a higher level. One of the major differences between novices and masters, the ability to quickly scan and understand code, flies out the window if the code isn't structured consistently and readable. Being lazy about coding conventions does more than just look unprofessional, it makes it more difficult to understand what's going on and leads to more bugs in the codebase.
This doesn't mean you have to recode your entire codebase in hungarian notation and implement a 100 page style guide for every project - but make sure you pick conventions early on and stick with them. It's more than just an aesthetic advantage but will lead to better software in the long run.