Freezing a texture projection does the following:
Cuts the association with the texture support object if there is one, and deletes the support if it is no longer used.
This reduces memory and processing times, because the projection no longer needs to be calculated but can simply be read from the explicit UV coordinates. You can continue to make modifications to the UV coordinates in the texture editor.
Select an object whose texture projection you wish to freeze.
Alternatively, you can right-click on any operator in the texture projection stack in an explorer and choose Freeze to freeze from that point down.