There are many other great uses for some of those oils other than just diffusing. I know very little about it (not enough to sound like I know what I am talking about), but my wife is an expert. She sells the doTerra brand of oils and mixes up her own blends for different uses based upon some oil recipes she has.
We have a few diffusers in the house and she often puts in some soothing blends at night to help sleep. I never get the benefit from those because I have to sleep with a CPAP machine/mask and cannot smell any diffusing aromas.
But as for other uses: two personal stories = (1) a few years ago while waiting several weeks for a really slow surgeon to schedule a gall bladder removal surgery, I used an oil blend called DigestZen to ease upset stomach symptoms and it worked really well to get me through the storm. I don't know what all is in it, but it can ease a lot of different stomach and intestinal discomforts just by rubbing a drop or two on your abdomen. It has a strong licorice-like smell.
(2) our daughter sometimes has a really bad reaction to things touching her skin - if someone scratches her arm with their fingernails, it welts up in seconds and causes really bad itching and hives. I think the doctor called it uticaria. She took zyrtec for it, but that didn't always work and would wreak havoc on her hair - drying it out and causing bad tangles (which resulted in tremendous tears and frustration when it came time to brush her hair for school). My wife found an oil blend called Tri-Ease that our daughter takes orally and it works ten times better than the zyrtec ever did without the other side effects.
There are MANY more uses for different oils that I can't speak intelligently of. I could offer a link to some information offline if anyone is interested, but don't think I am allowed to post it here as it does include referral benefits to my wife. One thing she would say, though, is to be careful of some of the cheaper oils at WalMart and Meijer stores as they are sometimes misleading in how they advertise the purity levels of the ingredients. I don't recall the specifics, but something like "100% pure" on a label doesn't mean that it is 100% of the oil itself without fillers. I think because they are not under the regulations of the FDA, they can be very misleading and give you extremely diluted product at a very cheap price.