Need help using my diffuser

[Komodo]

I just purchased a UFL-1 Olympus strobe for my underwater camera.
It came with a removable diffuser. I noticed that on my underwater camera case the diffuser is not removable. In the strobes user’s manual it tells me how to remove or put on the diffuser but nothing about when to use it.
I know the diffuser reduces the intensity of the light emitted by the flash, creating soft even lighting. My question is this, whet are the conditions for using or not using a diffuser. Do I simply keep it on all the time?
Is there anyone out there that has any experience with diffusers that can help me?

[AaronC]

It is highly recommended to use the diffuser when shooting wide angle or extreme macro images. In wide angle photography, the diffuser can be used in order to spread the light more evenly and in a way that it covers a greater angle. In macro, the diffuser can be used to absorb part of the light when the flash is too powerful.