This use of the UPDATE function for selective logging can be very useful when used on tables with columns such as: LastOrderDate, LastLoginDate, etc as these columns are often updated but those changes are probably not required to be logged.
One interesting point is that even if our trigger was configured to fire on DELETEs, the UPDATE function would not return true and therefore the change would not be logged. This makes sense as a DELETE affects all columns, so checking for a particular column is not required. If we wanted to log DELETEs to our ProductPriceLog table, we would use a trigger that fired on DELETEs.
But check the comments to make sure you know when UPDATE() fires—it’s not just when a particular column changes values.