comes a sewing machine. It's just part of the progression.
It seems most UL hikers start out examining ways in which to alter their BP experience by radically shifting focus to weight & utility. What typically entails then is a generation of expensive, traditional gear gets placed in the rafters, or given away to friends/charity, as the intrepid BPLer starts swapping out gear.
The next stage is discovering that a lot of 'commercial' UL equipment, while lighter than REI, isn't really UL; it's more like 'lightweight'. So, another, maybe significant, investment is discarded as the now (hopefully) wiser UL person begins to examine some of the many cottage offerings.
This, as many who have reached this stage, is the moment of truth. That's because now you can get "true" UL equipment, the kind of stuff that will help you to get way under 10lb base, maybe even near 5lb. But there's a hitch - it might cost and arm & leg. As an extra bonus, this UL equipment has a limited half-life, so it's not only more money, but it's less sturdy.
Enter the final stage: MYOG. MYOG won't really save you money if you're counting the value of your time invested in the project. But, if you're designing/sewing during non-billable/productive (ie work) time instead of watching TV, it's probably a better use of your time anyway.
However, I would have to say the real benefit of MYOG is finally becoming fully intimate with all the ins & outs of the various fabrics, coatings, functions, etc. Much more than saving money on material, MYOG is a graduate degree course on what really works, why and how to use it.
It forces you to understand the principles of CLO values, why you need to insulation/loft when @ rest/sleep vs why you need wicking/wind break material when moving. It drives you to consider down vs syn fill; it makes you think about what a pack can be, and how they might designed for very different specific purposes.
I'm not suggesting your friend begin @ this point, rather it's just an observation that if you start on the UL journey (typically with the acquisition of a scale), it's difficult to not end up at this final point.