Crafting is one of those skills that people think they can live without. That's no where near the case. Crafting helps in several other skills such as Herblore, Most Combat Skills, Cooking, Farming, Fleching, WC, Prayer, Runecrafting, Firemaking, Range and Construction. As you can see, Crafting plays a very big part in our normal activities, be it planting a yew tree or fighting with that battle staves you just made.
Fun Stuff for the Higher Levels
Once you reach one of those higher levels in crafting (70+) you will easily be able to make some useful items. You will be able to craft black d-hide range armour for the range enthusiast. Making battle staves will help much more in magic as they give a larger bonus, as well as being strong enough to be used as a melee weapon when you run out of runes. Making your own vials for your potions will be a lot easier and a lot cheaper then trying to buy large quantities from the GE. Have you finished nature spirit but lost your Blessed Silver Sickle, well don't fret because you can just make a new one!
There are many more things you can do with crafting but I wont bother adding them all. Go and discover all the uses!
Final Notes
At level 40 you gain access to the Crafting guild! This guild is very useful when you need molds but don't want to pay. Don't forget your brown apron.
If you don't want to go to Entrana to get you glassblowing pipe, you can always go to Hemenster.
Thanks for taking time and reading my guide.