Exactly so. The one fly in the (all suburban trains) 701 thinking that has crossed my mind, is the need for main line diversionary route knowledge for weekend engineering work, primarily via Chertsey. Basing depot has always played a large part in this, as the likes of Woking/Waterloo etc would not be able to cover everything on top of their own work.
Thus far a couple of Weybridge return trips have been covered by 450's worked by Basing for this very purpose.
To my mind it's completely unpracticable to train xx bodies at Basing on 701's (this is when someone with closer hands on tells me they are..

!) both in cost terms and in traction knowledge retention, unless there is a plan to 'pass' crews between, Basing and (eg) Woking to give them a greater degree of 701 work.
Otherwise with 450's still visiting Clapham Yard between the peaks (off main line work) it may be that some of these be used for a couple of return trips to Weybridge via Chertsey, for the benefit of Basing depot's retention of route knowledge?