Re: Treatment of IFR flight plans (UK, outside Class A)
LARS units, as has been said before, have no interest in en-route charging.
The unit I'm talking about has such a large turnover of traffic that it often refuses prenotes/handovers due controller workload, but having FPL details available reduces workload when the pilot calls. Sometimes, even people who don't file FPL's phone beforehand and pass brief details (to an assistant) which is also very useful.
Additionally this unit is often asked to open/close FPL's, which it does workload permitting; in these circumstances it's also useful to have a copy of the original FPL.
What they can't do 'cos they're so busy is action AFIL's (see separate thread in ATC section)