Each of the plug-in can be installed individually. So, you don't need to install all of them if you don't need any of the plug-ins. I guess you know already the usage of these plug-ins from their names. For example, Applications and tasks displays the list of application and tasks running on our phone. You can also display detail information about applications or tasks, such as the UID, capability, stack size, etc.
Y-Tasks is developed by Jukka Silvennoinen a.k.a. symbianyucca a.k.a. Dr. Jukka. He is the developer of Y-Browser, one of the popular file manager for S60 3rd Edition. If you are participating in Nokia discussion board, you may also have heard his nickname many times.
Y-Tasks is collection of development helper tools. However, some advanced users may find it useful too. It consists of several plug-ins, i.e.:
- Trace
- Crash monitor
- Applications and tasks
- File types
- Fonts
- Memory status
- Processes and threads