I like to buy equipment (when I can afford it) because the less I have to rely on equipment that I haven't used before (i.e. that I don't own), the more peace of mind I have. Example: If I build a show that uses a MIDI-USB interface, I'll buy one so that I have it for the tour and for future projects. Plus it lets me experiment on my own with test-builds, rent it out to other designer friends when I'm not using it, and often times having certain bits of tech in my "just-in case" kit has saved the day for more casual/low-stakes projects, pieces, installations, and VJ setups (both mine and others) where everything hasn't necessarily been thought out meticulously ahead of time because ideas are still evolving in an organic way on site. It also has helped me in cases where there's been dud rental equipment or other equipment failure and new equipment is needed too last-minute for rental (or even purchase) to be an option. (Also I'm secretly a dragon but my hoard is equipment, not gold.)