An ability to output detailed 3D renderings in a reasonable time-frame can give you an edge in a fast-paced concept design industry for films and video-games.  A 3D library of pre-modeled mechanical parts becomes extremely applicable due to iterative nature of entertainment design where an artist has to output multiple versions and address client's notes/changes effectively within tight deadlines.  

-What are the benefits of having a library of 3d kitbash parts?

When it comes to creating detailed 3d concept designs having a library of prebuilt 3d kitbash parts can save you days of modeling and it makes it a lot faster, easier and just more fun to build concept designs in 3d. The final stage of finishing a complex mechanical design can be especially costly on its timeframe as there is never quite enough time to push the level of detail to realistic level. The goal of 3D KitBash store on is to provide variety of sets  of reusable generic mechanical parts that will help you to finish your own concepts much quicker and therefore allow you to spend more of your time on creative things that matter the most, such as overall silhouette, balance, proportions, flow and of course experimenting.