Employees who have unrealistic expectations from the start generally keep that same level of expectation, even across other topics; beginning with an unrealistic figure is not necessarily a good idea, as it may dissuade the HR rep. Alot of the time this is a first question too - first impressions count! </cliche>
Nb - this may be different for engineering; I work in an unrelated field.
I guess the issue could be though, if the employee is fresh out of college or moving into an unrelated position, that they may have no idea what a good salary for this position is going to be. I guess the danger of being to reasonable is that you will end up with the job, just underpaid compared to your peers because you didn't know what that market rate was.
Nb - this may be different for engineering; I work in an unrelated field.