Oracle Triggers - Before Update and Before Insert - Separate or Combined?
The actions you're performing on the data is technically different between the insert/update portions, but what about the business logic difference? IMO, your best bet is to contain a functional unit of work inside of a trigger, so that there is no discrepancy in what that trigger does. In my experience, Developers/Business Analysts often tend to think in transaction workflows.

I have found this to be especially helpful when I or others have to troubleshoot the consequences of user data corruption as it relates to triggers being fired - the less triggers you have to try to piece together the logic for, the easier it is to see how data was manipulated.