So I know in at least one of the previous games, using the Axii sign in dialogue had tangible effects on how efficient it was later on.

You could "bump" your Axii ability by using it more often, and it would let you do stuff later that you couldn't do otherwise.

Is it the same in The Witcher 3? There's an early fight where I want to just tell the guys to go screw, but I'm tempted to use the "Axii" dialogue option just because I'm worried if I don't I'll miss out on an early easy Axii use that will make the skill better later on.

Or is all Axii skill development done through using points / EXP and NOT from actual use?

Great thanks!

In one of the games (I think it was Witcher 2) you could get "perks" or whatnot from actually successfully using the ability so it sort of behooved you to use it if you could.

I was afraid I'd miss an early easy success and unlocking a "better" Axii but if upgrading is handled fully by assigning points I'm good to go!

Pro tip: Search out and use places of power. The first time you use one it gives you 1 ability point to spend. You also get them from leveling up.