An even important disadvantage is that you're allowed to take up to five lessons per one experience level (you can complete all five lessons with the same trainer or choose different trainers). Each lesson costs a lot of gold (typically a few hundred coins), so you must be rich in order to ensure that you can use trainer's help on a regular basis. As for the disadvantages, one of them are the costs. It's worth mentioning here that completing lessons and increasing skills counts towards the progress needed to advanced to higher experience levels, so you can also work on improving the speed in which your character gets stronger. The biggest advantage of this method is that unlike with skill books you don't have to waste a lot of time exploring the world for new items, because you can always to return to the same person.
Visiting skill trainers is a very interesting way of developing main character's skills.
