line conditions are available on a line Behavior section when you have one or more lines coming out of a single activity, like a decision gateway. In the following diagram Line 1 and Line 2 are branching out of Step 2
Line 1 is default and L2 needs a condition to be satisfied on the other hand in a decision gateway approach
we use a exclusive decision gateway to do the same, if more than one line evaluates to true a split happens, in case of a simple BPD where we want a exclusive scenario decision gateways are used in place of line conditions because the order in which the line conditions evaluate is not guaranteed, but I have seen line conditions for splits in multiple projects. If any other line besides default evaluates to true default path is not taken but if besides default line there are two or more that two lines evaluating to true process takes all the paths and multiple parallel tokens are created.