A friend of mine had the same question: why updating when everyting works. Until the moment he needed to play in a studio, and his laptop with RB 4.5 did not recognise the NXS set. Some studio enigineers tried their best, but the problem could not be found.
The reason why he never updated RB, was because his older laptop with older Intel CPU could not install the latest RB SW version, becasue it's 64bit. I installed the RB 5.5 32bit version on his laptop via this link.
RB 5.5 not only has the new and better visible layout, but it also solved the link issue in the studio. RB 5.5 instantly showed the 2 CDJ's and DJM, so he could continue using any NXS set on his laptop.
Updating firmware, even when your hardware is running perfect, is not for the show. Firmware often contains improvements, and bug fixes users and Pioneer engineers found. Maybe not Always that important for every user, but again, firmware updates are often mandatory for good working hardware.
When you analyze tracks in Rekordbox, and you add CUE, loop, etc. info, you can save all that information as a back-up. I can explain this with many words, but it's better to watch some YouTube tuturials about this part, as this is easier to understand.