In the particular example you use, no difference, you are obtaining the value and comparing it with a set of values.
The second syntax form, however, allows for the following, whereas the first only retrieves the field value:
Conditions can refer to properties of objects using a SPEL syntax (Simplest Possible Expression Language). For example, this enables you to build a Condition that tests if a field is displayed or not. These expressions take the following general format:
Internally, the SPEL expression is a cover for Oracle Forms builtins like GET_ITEM_PROPERTY, GET_BLOCK_PROPERTY, etc. Additionally, the SPEL expressions support retrieving Profile values, Message Dictionary text, and Local Variables (described later).