In what ways do you take advantage of Ash's respec?

[thomson1]

I'm assuming it doesn't allow exploits like: train a +4 apt skill, transfer to a -4 apt skill for a "net gain" of xp inspite of the -20%.

Naturally there's the possibility of "hey look I found a new weapon", and maybe not bothering with T&D in the early game and then dumping xp into that when Zot traps start popping up, but other than that, what's it for? Are some skills so hard to victory dance that it's better to sacrifice xp from some other skill?

[galehar]

There's no exploit with aptitudes, nor with crosstraining. If you transfer from high apt to low apt, the receiving skill will just gain less levels.
Using it to train skills instead of victory dancing can be convenient, but it's not optimal. The point of it is more to allow you to change your strategy depending on books and weapons you find.

[mrbobbyg]

It made a lot more sense imo, when there was a big exp bonus from Ash. That way you could flexibly reskill with ease, which was a nice contrast to having inflexible gear.

[KoboldLord]

boost spellcasting, because spellcasting!
bootstrap evocations in order to make use of elemental staves, because you have no use for low skill levels
bootstrap dodging, armor, shields, or stealth because those are seriously obnoxious to train
No low-level training spell found for <magic skill you want>? No problem!

Probably nothing else is worthwhile, because you can just victory dance it.

[7hm]

My Ash (/BE) strategy.

1) Start a berserker with decent spellcasting apts. My favorite is HE.

2) Switch to a weapon that allows buckler usage (to maximize defense), I prefer long blades in general, with HE in particular.

3) Get a great Trog gift by the end of Lair (this is ideal, sometimes Trog doesn't oblige, in those cases just get a good Trog gift).

4) Dive through the lair rune branches and burn trog piety in the end vaults.

5) Drop Trog. You should be around turn 25-35k at this point.

You now have two options:
6a) Wait out Trog's wrath by building up a popcorn shield of piddly monsters on the low D levels. This takes 30-45k turns. Ring of sustenance recommended.
or
6b) Get cTele and learn blink / teleport self asap (or get a wand of teleportation). No waiting for you, you're doing it the manly way!

7) Switch to ash.

8) Get good ash piety and as soon as possible start pumping spellcasting. Should be able to get up to level 6 or 7 fairly quickly by dumping your pointless skills, like stabbing, or weapon skills you didn't use.

9) Pump up your primary magic school. Again, this should be fairly quick. Though (as my current game is teaching me) you do need a bit of luck to get a book that lets you cast an early spell from that school, because you do need that 1st level to be learned normally.

10) Cast tornado with a character with 200+ hp that can melee pretty much anything.

[dpeg]

It made a lot more sense imo, when there was a big exp bonus from Ash. That way you could flexibly reskill with ease, which was a nice contrast to having inflexible gear.

We have explained a number of times why a plain xp boost is not as desirable. The reskilling makes you think (along the lines of this thead) of when/how to use it -- the xp boost is passive, but is otherwise metagamey and opaque.
A typical reskilling usage is to adapt to the books you find. One instance: if you start a VM (a great background to get you through the early game), you can decide to put all of your Poison Magic skill somewhere else, the target depending on what you've got by then. Another one is switching weapons; the stunt explained here about exploiting Trog sounds pretty advanced already.
The goal is not, and never has been, to have player reskill all the time. It is a strategical ability, increasing your flexibility. In a given game, you may never (have to) use it. But it's always there.