Oddly enough Willesden depot seems to be far better connected to the WCML▸ slows than the Euston/Watford DC▸ line and the NLL▸ , I guess it used to have more of a role for the WCML in the days of Silverlink.
Willesden was built as a ETMD (Electric Traction Maintenance Depot) by
BR▸ it serviced the main line electric locomotives for the WCML, the rolling stock was (is) maintained at Wembley, now that the WCML operates multiple units ie Pendilenos Willesden is not needed although before LO took it over it was used by one of the
FOC▸ 's
Willesden used to do some of the heavy repairs to the old Euston Watford Units and some were stabled there but as you said it is a pain getting them in and out, whether LO and
NR» have plans to change this in the long term I don't know.
Willesden Depot was also the site of a ECR (Electrical Control Room) its control area was transfered to Rugby as part of the WCML upgrade about a decade ago