The reason this node exist is because you can’t connect 1 exec output to 2 or more inputs because it impossibe to reliably control execution order, you need to define order of things and this node alows you to do so.
Other reason to use it is ability to create a sequence of node that breaks and code can continue from the sequence. If you do normal chain of nodes once code execution breaks (for example failed Branch or Cast) it’s over, function ends (technically events are also functions), sequence allows you to continue execution from different point once something breaks on one end