What is the difference between the SAP Script texts, 'Customer &KNA1-KUNNR&' and '&Customer KNA1-KUNNR&'?

In the first case of 'Customer : &KNA1-KUNNR&',
the text 'Customer : ' is displayed regardless of the variable KNA1-KUNNR even if it is having Initial value.

In the second case of '&Customer : KNA1-KUNNR&',
The text 'Customer :' and KNA1-KUNNR is displayed only when the variable KNA1-KUNNR has non-initial values.