If you're in a construction mode other than Animation, you will get this warning when you try to set an envelope on a deforming object.
If you click Yes, Softimage applies the envelope in Animation mode so that the Envelope operator is in the Animation region of the envelope's construction history.
You need to be in Animation mode to apply an envelope if you want to use envelopes with a skeleton to animate a character's skin, which is the most common reason to use envelopes.
If you click No, the envelope is applied in the current mode:
If this is the case, which is less typical, you are using the envelope's deformations to sculpt the geometry and do not intend to animate the envelope.
If you're in Shape Modeling or Secondary Shape Modeling mode, the Envelope operator is put in the envelope's Shape Modeling or Secondary Shape region.
If this is the case, which is less typical, you are using the envelope's deformations to create shape keys and do not intend to animate the envelope. The Envelope operator will be deleted when you save or apply shape keys (create shape clips in the mixer) unless you first mute it. To do this, you can choose the Deform > Save Shape Key command.
For more information about construction modes, see Construction Modes and Regions [Modeling and Deformation Basics].
