is there any advantage to use lighter armor over heavy ones (without going over 70% weight ratio)

[Dweller Beyond the Threshold]

If I wear heavy armors and not go over the 70% ratio (I probably have to spend few points), you could get much better defense and the speed is the same. So beyond the need to spend few points (which grants you better defense anyway), I really don't see the point of using light armors as they really don't allow much margin of mistake.
Unless you spend more stamina while wearing heavy armor? I haven't noticed that though.

[Tautou]

Fashion

[Bazzy]

Rolling and dodging for the most part.
It's a matter of playstyle imo. I'm personally hate the tank-y slow playstyle and fat rolls are a no go to me - but the thing i hate already is no longer being able to upgrade the armor like in ds1 before and so i have to switch the armor to a 50% weight now, i'm playing merc class.

[Arngrim]

Heavier armors give slightly better mitigation, but it may not be worth the stat investment.
Ppl are saying you get longer roll distance the less load you have, but I havent tested it myself.

[Dweller Beyond the Threshold]

Originally posted by John Snow:

Rolling and dodging for the most part.
It's a matter of playstyle imo. I'm personally hate the tank-y slow playstyle and fat rolls are a no go to me - but the thing i hate already is no longer being able to upgrade the armor like in ds1 before and so i have to switch the armor to a 50% weight now, i'm playing merc class.

but that's not the case if you don't go over 70% threashold. I have the exact same rolling/running speed wearing heavy armors and light armors as long as my weight ratio doesn't exceed 70%.

[Cormac]

based on the DS3 wiki:
over 100% load: no backstab and no rolling
70%-100% slow backstab, fatroll (very slow) 12 iframes
30%-70% fast backstab, medium rolls, 13 iframes
0%-30% fast backstab, fast long rolls, 13 iframe

so basicly, as long as you stay below 70%/30% load, you gain those benefits, no matter how heavy your armor is.
on the other hand, it all depents on your build. do you use 1weapon+shield, get the heavy armor, you are using 2 weapons, 1 shield, 1 bow and 1 caster item as well as 2 different arrows? you may be limited to some light armor.
you don't want to level up the load? again, light armor
also: some light armor have some special resistances, like the cleric blue robe (high poison and curse resistance) which you may want to use in some areas. but in the end: as long as you stay below the 70%/30% limit, you can wear whatever fits

[TisEric]

The only difference between 0% and 70% load is stamina regeneration.
After 70% you start slow rolling and after i think 120% you cant roll at all.

FYI armour , like in DS2 , makes basically 0 difference.
Unless you wear the super heavy stuff with a great shield you wont even notice the change.
If you like rolling around ( at the speed of sound) and generaly being a fast character anything that keeps you under 70% is good.

At that point its just for looks.