Im currently doing a Cert 2 which is one of the shorter courses I think Lara is refering too and in the 2 weeks Ive attended so far I have learnt SOOOO much.
Not just sanitation and hygene practices, but risk assessment, what skin conditions I can safely apply makeup to and which ones I should stay well clear of, basic colour correction, contouring and a whole lot more. Then there is the colour theory which can be complicated, I have an art degree which helps me on that but the colour theory you learn in classes is a HUGE help, not only on understanding how to apply colours so they look good together, but also with camoflauge and concealing again.
If you ever wanted to work as a MUA in another country, say on a working holiday or something, you may find it easier getting work if you have some kind of formal training. In some places you may have to have some kind of certifercation to work as a makeup artist even on a cosmetic counter, and in other places while it may not be a legal requirement it does make getting work a lot easier.
Also, I know a lot of pro MUAs like Lara who wont allow you to assist them without the certifercation. Its tough to break into this industry and you really want to have every edge you can get and formal training helps you get that edge.
In the end its up to you, where do you want to go with this and how much are you willing to sacrifice as far as time and money goes. In the end while you could get away with not going to school, its a good idea to go. Even if you only do the units covering sanitation etc and get a certifercate of attainment for those units. But for me it really is a must.