The Update([column]) function can be misleading. It will tell you whether a column has been updated, but will not tell you whether the value was actually changed. So, if you issue an update against a table then all the columns in that statement are considered "updated", even if their value did not actually change. Considering that may applications write an entire record to a database rather than issuing an updated only for the modified columns, using the Update() function can lead to a lot of false hits.
A more accurate method is to compare the values from the INSERTED and DELETED tables to see whether your column value actually changed.
If it's not practically useful, then it's practically useless.