One of the things that is attractive about metal construction is the ease with which structural modifications can be made. What would require substantial amounts of design, planning, physical work and cost in a GRP boat can require very little effort in metal, whether steel or aluminium.
A good example of this is the installation of watertight bulkheads. When we had Pèlerin constructed we specified an additional full depth watertight bulkhead aft of the anchor locker. As the angled back wall of that locker already formed an effective watertight bulkhead it might seem to be overkill to add a second one, but in fact the anchor locker bulkhead is too far forward and so doesn’t extend far enough below the waterline, and as there was already a designed ring frame behind it, (a) we weren’t going to lose much additional space and (b) all that had to be done was provide a plate to ‘fill’ the ring frame to make it fully watertight. The cost was in the order of $100—negligible on our boat.