Default values — how trivial this hint might seem…
Although, simple things make life easier. If you have a huge amount of SQL updates in your system, having correct default values helps to build smaller queries.
Also, when playing with data in your PhpMyAdmin, you can afford to focus on what is really important, not on repeating the boring staff. Every time when you have a big table and need to paste a couple of new records manually, you or the pear developer will be thankful that the majority the fields can be just ommited in order to have the proper and meaningful value.
It can be zero for numeric types, current date and time value for timestamp, a most frequent and meaningful value for the ENUM field or a “magic constant” of default value if you have to use one in your application.