Conflicting solutionsThe most obvious reason is another company also wants to use the same values as you. This will go unnoticed in custom fields, but as soon as you both customise the values of an out of the box optionset, like accountcategorycode, you'll quickly run into problems. Let me show you what happens. In the following example I set up a couple of new options on accountcategorycode and changed the value of "New Option 1" to 3. I have left "New Option 2" as it's recommended value for the purpose of this sample:
Another publisher is also using these same values rather than the recommended in a managed solution. What you end up with is an overwrite on the options with the shared values:
As you might notice our option "New Option 1" has been renamed to "Other 1". This might not seem detrimental in this particular example, but what if the change was from "Bad Debt Customer" to "Most Awesome Customer" or something to that effect. This should be enough to prevent people from doing this, but unfortunately it's usually swept under the carpet as a really unlikely scenario.
Status CodesThe next issue is inconsistent usage introduced due to fields like status code. You may not realise this when you embark on your adventure to ignore the CRM recommended values, but you cannot apply this standard to all option sets, in particular status codes:
CRM disables the value field so you're stuck with what it recommends and you've got an inconsistent standard. So should you just make an exception to use recommended values for status codes, but continue on your own standard for other fields? Or do you extend this exception to all out of the box fields? There are few things I hate more than inconsistency in naming and value conventions so I say just stick with the CRM recommended for all fields.
Annoying message boxesThe next big reason you shouldn't do this is it becomes incredibly frustrating to add new options to an optionset if you want to maintain this standard. Even more so when you're adding a lot of new options. You will get bombarded with a message like the following every time you change the number for an option: