All instruments that are brand new or pre-owned benefit from being tailored to your specific playing wants and needs. Most instruments have a generic setup when bought from new and preowned instruments are tailored to the previous owner.
Tailoring an instrument to you helps you get the most out of your new guitar. With three big plus points!
Instruments need a setup to work, but it may not be exactly what you require. The guitar/bass/ukulele, could sound perfectly in tune, but not be enjoyable to play. Getting a guitar setup to the players specific needs makes the instrument easier to play.
Better playability helps you progress further. Certain technical exercises can be executed more efficiently. For example pressing the string against the fret could be a much easier task. In making this task easier, chords have more clarity and because it is easier (causing less strain) you can practise for longer with less pain.
Instruments need caring for, in the same way your car gets a service and MOT. The strings exert a tension on the guitar which makes it harder to play if not regularly serviced. New strings, a full clean, setup of the instrument to you and electrical clean keeps your instrument in the best possible shape, all included in the Setup.
For Every Guitar:
The far right is a brand new Les Paul that needed tailoring to be a much better player for it's new owner, that was around £2000 new, in need of a setup. All Guitars from £10 to £10,000 always benefit from being tailored to the person playing them for the best experience.