Why using a puncture repair kit instead of a new inner tube?
You have to remove the wheel to replace the tube. A repair can be done in the frame.

On older bikes without quick release, and with current gear hubs, electric hubs, Nuvinci hubs, belts etc, you need a spanner and oftentimes, the gear adjustment goes back different and needs fiddling with. 

This reduces the advantage of tube changes. A fix is only 3 mins.

Hints: 


Once opened, small tubes of glue dry out very quick, so I always have an unopened tube in my kit. 
I also find that using the aluminium foil from the patch, over the tube opening, and screwed under the cap, keeps the glue alive longer. 
real sandpaper beats the hell out of the useless punched metal scraper thingy
you should have a square of canvas or equivalent for covering splits in the tyre sidewall