maybe stupid question but I need to ask

[DonVito]

Hello all !!  https://www.triumph-trophy.com/Smileys/light/158.gif

need to know if this cap is doing some purpose ( like holding handlebars  and etc  ) or is just there because is very good looking and that can be easy taken off if needed

https://cdn.img.triumph-trophy.com/IMG_20190520_211341ad38074c50a6c63d.jpg

Thx !!

[GavJ]

This cap holds the top clamp onto the steering head, fairly important,,,,, I wouldn't ride with it missing 🤔

[Coconut]

That is the "Headstock Top Nut" and secures the Top Yoke ( which the Handlebars are bolted to )
to the Steering Stem. 

If the Headstock Top Nut nut is removed, the Top Yoke complete with handlebars,
can be lifted off the Steering stem.

It should be tightened to 90Nm 

[rpeters549]

Yup, what they said.
Should you run in the unfortunate wire pinch separation breakage issue, that nut pulls the top part off the handle bars bolt to and contains the ignition set for the key.

[DonVito]

had  to ask because a had 2 bikes few years back and on both of them " the CAP" was just for the looks   and there was a nut that was  actually holding everything in the place underneath .
Thx for your  time guys  and help