That's the fresh air side of the pcv valve system. It's important. Without it the engine will run lean, allow unfiltered air in, and if you plug it the pcv valve will stop working and you'll start blowing out seals.
If the hose is disconnecting from the PCs valve, a small hose clamp should work. If the POV valve keeps popping out of the valve cover, etc may help or you may need a new grommet to hold it tighter. May also want to try a new PCs valve. If it’s stuck closed, Maybe crankcase I pressure is pushing it out.
From the picture provided there is no clamp on the hose at the filler neck, valve cover side of the hose. The hose appears to of had one there at one time so I recommend putting a worm clam on it just to help hold it on. RTV sealer could work but unnecessarily messy for no reason. Also be sure to check the PCV valve to be sure it is not plugged causing a build up of pressure in the crank case popping this hose off because it is the weakest point.
In short install a worm clamp and check PCV for proper operation ( should rattle when shook) and problem will be fixed.
It popped out of the valve cover, so I couldn't hold it with a clamp. I could still push it there, but it was quite loose. I found one at a junkyard, fit much tighter and so far hasn't popped back out.