[throway_foo_bar]

> if you have to use a throway foo bar

Ad-hominem.

> It's as a curtsey but don't think it's necessary.

The job hunt process is lubricated with politeness. Both employer and employee should want to make a good impression on each other; like on a first date. I can't imagine a situation where courtesy was more necessary than that. More so, when it costs next to nothing to send out an AUTOMATED email

1) Acknowledging receipt of an application and thanking the candidate. [Enables the candidate to keep records in a busy life]

2) Informing them you've moved on, and how soon they are allowed to apply again [Typically >3months].