As a low voltage contractor I believe it is very important! The biggest thing I tell contractors about prewiring is that wire is cheap. You’re much better off throwing in the wire anywhere you “might” want speakers, data, alarm, etc. because it’s better to have it and not use it than to want it and not have it. Once the house is built then you have to tear up drywall, or go through your attic/crawl space which is much more expensive and time consuming. Now there is a lot of wireless stuff out there but hardwired is still the best option. I hope this helps. Also, please make sure to get a qualified low voltage contractor to design and do the job.
It is extremely important to the wire-man in terms of labor intensity; or ease of installation and accessibility. I would feel it also opens the door to more creative options in designing the install to an optimum quality with provisions for future adds or changes etc., such as running flexible conduit tubing in wall cavities from outlet points to at least non-public accessible areas such as an attic or crawl space. However it can still be accomplished without pre-wiring but it can makes things quite a bit more challenging on labor, sometimes requiring an additional person. With no particular code or safety requirements that I am aware of pertaining to this question I think the importance of pre-wiring is relative to contractors’ costs and labor. Hope this helps… Happy Wiring!!!