I've been cutting my daughters' hair for the past 6-9 months. I'm much better now, and the detailed videos on YouTube were a huge help. The first cuts were okay, the second were good, and the last ones look excellent - as good as most cuts from a salon. My oldest (6) keeps her hair mid-long, so it's a pretty easy trim, but for my middle daughter (3) I tried an angled bob this last time - short in the back and an inch or so longer in the front - and it looked really cute and grew out nicely. It's definitely more challenging to cut hair shorter than long. I always think that even if I can only do every other cut, it still cuts our haircutting costs in half.
Cutting my own hair did not work out so well - the first time was great, second time fine, but after the third it looked awful and it took two trips to a proper hairdresser (12 weeks apart) to fix it. I have curly hair, so I think it takes more specialized expertise to cut it so that it doesn't frizz and is low maintenance. I only need to get it cut about twice a year since I only wash once a week, never use a hair dryer, and very few products.
My husband has very curly hair, and a professional type job, so he looks better with a proper barber, too. I'd be willing to learn, but haven't found any videos for his hair type online. With a bad haircut, he looks like a chia pet after a few weeks.