The behavior of NULL concatenations is actually a connection setting. By default, NULL concatenations yield NULLs, but that can be changed at runtime by using a different connection option. It so happens that Crystal Reports (at least earlier versions...) used a default connection setting that allowed concatenation of NULL values. I can't even remember how many hours I spend trying to figure out why the hell my simple code would return one set of values in Query Analyzer and a completely different result in Crystal Reports!
If it's not practically useful, then it's practically useless.