Each practice you put in skill common to adventurer and your final class is in theory one more practice points you can save for HP trains.
You might get an extra train at 50. 10 HP's 
Hardly worth much, unless your race/class has really low con or they share a lot of skills with adventurer.
But then again Adventurers have lower max rolls at character creation, which offsets this, unless you do not use any trains on stats.
This will leave you with a PC with 9 or less stat points holes, higher HP pool and the need to use a crap load of gear to correct stat until you can fix it.
Of course you should be going full 1 prac.
In the end it's a nightmare, and your fully trained Fire giant will be shelved because you got burned just training the darned thing.