Developer Exploratory Testing is (briefly) when developers from the software team test their own application. Davor Crnomat explains it (and some more) from a tester’s perspective in this Øredev session video.(http://oredev.org/videos/test-manager-in-an-agile-team) I, as a developer, have my own reasons for loving DET.
1. It is almost like a video game
The objective is to crash the program. Find the most creative ways to do so and then identify the core to make it reproducible. You could make a game of that!
2. You get to know the framework, platform and environment.
It is one thing to read the documentation and produce unit tests, but by using the software you really get to know the weak spots of the environment that you work in. So then you know what pitfalls to avoid the next time and you can concentrate on learning new fun stuff.
3. Share knowledge in the team
To find a bug is one thing, to solve it is something else. But if it is your very competent colleagues that find the bugs you caused there is a chance that they know how to fix it as well (since they’ve been there and done that). The bugs that you, as a team, find but can not solve on the spot, can later be revisited as one of you solve it and then all of you will know what to do the next time this problem occurs.
Find the bug before someone else does. Then you can fix it and no one will know (except your buddies who have learned from your mistakes). Sometimes there are bugs that can not be fixed. Then you know about them, and can explain why they are not already solved, as someone outside the team finds them.