I don't understand the difference between generateEscapeBlock="whenNeeded" and generateEscapeBlock="always"

[Costello, Roger L.]

Hello DFDL community,

I have an input file that uses a colon to separate (delimit) fields.

The backslash symbol is used to escape the colon.

Below is how I define the escape symbol. Everything makes sense to me except 
generateEscapeBlock. I get the same behavior regardless of whether I use 
generateEscapeBlock="whenNeeded" or generateEscapeBlock="always". I read the 
DFDL specification description of generateEscapeBlock. Honestly, that didn't 
help in my understanding of the difference between whenNeeded and always. Would 
someone please explain the differences in simple, layman terms, please? When do 
I use one versus the other? When would I see a difference in behavior?  /Roger

<dfdl:defineEscapeScheme name="Backslash">
           <dfdl:escapeScheme
                        escapeKind="escapeCharacter"
                        escapeCharacter="\"
                        escapeEscapeCharacter="\"
                        extraEscapedCharacters=""
                        generateEscapeBlock="whenNeeded"
            />
</dfdl:defineEscapeScheme>