This is speculation, but a couple features on the site linked in the question stick out as requirements likely to drive the decision to use Boyd bolts instead of other fasteners:
- "The design flown on Apollo required only a quarter turn for release"
- (from the patent) "means for preventing the nut and screw from unintentionally separating in response to vibrating forces" (i.e. these are locking fasteners, made to resist backing out in vibrating environments)
Combine that with
Various ALSEP experiment modules were attached to the two ALSEP packages with Boyd Bolts. In addition, the top surface of the Central Station was attached to the base by twelve Boyd Bolts, which had to be released before the top could spring up into its final configuration.
So you have things that need to stay attached during launch and the trip to the moon. This motivates a locking feature. However, they also need to come apart on the lunar surface, and an astronaut is supposed to make that happen. Traditional aerospace fastener-locking methods like safety wire aren't amenable to removal by a suited astronaut (the wire could puncture a glove!). The Boyd Bolt is, evidently, the solution accepted for that problem.
Is it supposed to be turned by hand, or by a tool?
Per the site, there is a "Universal Handling Tool" to be used by the astronauts on the lunar surface to detach the bolts. The quarter-turn release is to make that even easier.
Is the spring supposed to help attach things together, or detach things apart?
The spring is part of the locking mechanism that keeps the bolt attached. The website also mentions "a Boyd Bolt popped off when it was released" so it may have been used as a positive indication of fastener release so that the astronaut wouldn't have to fiddle with it while wearing the suit, but the main thing actually making it easier to detach was that it only required a quarter turn for release.