And even if you do file electronically - it doesn't give you any advantage
ATC will acknowledge the transmission and consider the request. If possible, and depending on traffic, workload etc, an ATC
clearance or alternative clearance will be then provided, which if acceptable to the pilot shall be read back in full.
3.10 The aircraft must remain outside any CAS until such time as ATC have provided a clearance and it has been acknowledged and
read back by the pilot.
3.11 Whilst there remains no guarantee that a suitable ATC clearance can be provided on every occasion that a request is
made, the pre-notification of Abbreviated Flight Plan details should enable some measure of pre-planning by ATC.
Having flight details available in advance should also significantly reduce the amount of RTF required to facilitate such
requests.
perhaps the last sentence is the only advantage - less RT.