Depends what you mean with 'directly': You can use stock Eclipse, as outlined as well in this series: DIY Free Toolchain for Kinetis: Part 1 – GNU ARM Build Tools | MCU on Eclipse
The advantages are essentially the same as for any other Do-It-Yourself project: either you use/buy something existing (faster, easier), or you do it yourself and get exactly what you want and need, but you have to invest time and efforts into it. It all depends what you want and need. And I think you only will know that advantages and disadvantages for yourself if you have done it. But I think if you read through the above series, you should get a pretty good understanding.
I hope this helps,
Erich