Three principle reasons:
The inner forestay has also proved used in allowing the forestay and furling system to be removed without first de-mounting the mast.
The shots below show one method of providing a secure attachment point at deck level for an inner forestay capable of taking the strains imposed from either a storm jib or a heavy weather No 3.
Note that in the photo shown below, the U bolt to which the Wichard adjuster at the lower end of the inner forestay is attached – is the one with the black feet aligned fore and aft. This view shows the forward face of the anchor locker bulkhead which has been strengthened by gluing a new piece of ply onto the existing bulkhead and glassing round its edges to the hull sides and underside of the deck. Before two stainless steel webs (fabricated by Bottomline Ltd) have been bolted onto each side of the bulkhead (the second picture below shows the inside face of the bulkhead within the fore cabin). Note that the athwartship U-bolt to which the wire jackstays are attached is simply bolted through the deck and is not attached to the new web.
View from within the fore cabin, note that part of the headlining moulding needed to be cut away before the stainless steel web could be fitted flush to the underside of the deck head.
This view shows the distance between the new forestay attachment and the mast head - distance should not exceed 7 inches.