AP accumulates during combat however I have yet to see a specific use for them. I see no weapons, signs, or skills that state the need for them. I do see throughout application of the aforementioned that AP will increase during combat as well as drain out of combat.
From the article Adrenaline - how to gain it and what is it used for:
Adrenaline on its own doesn't change anything. But it can cooperate with many skills, modifying them or increasing their effectiveness. Most important relations with adrenaline have:
Undying skill from the Combat category - Thanks to this skill when you lose all health points you don't die immediately, adrenaline points can be used to keep Geralt alive.
Rend skill from the Combat category - Adrenaline points can increase the amount of damage dealt even by 100%.
Deadly Precision skill from the Combat category - Adrenaline points increase the percentage chance of instantly killing the opponent.
Flood of Anger skill from the Combat category - Having enough adrenaline points allows you to activate the witcher sign on the highest level possible and increase the attack strength.
Hunter Instincts skill from the Alchemy category - Having the maximum amount of adrenaline points will increase the damage of critical hits. However, it will work only if an oil effective against a specific monster type has been used.
Rage management skill from the Abilities category - It allows you to activate witcher signs even if you don't have enough stamina. Adrenaline points will be consumed instead of the lacking stamina.
Focus skill from the Abilities category - One of more interesting skills. Thanks to adrenaline points Geralt can deal more damage and the strength of his signs increase.
Various other sources also mention a general damage increase the more adrenaline you have. From a post on CD Projekt Red Forum :
Each point of Adrenaline increases your sword damage by 5% So with 3 Adrenaline points your max sword damage is increased by 15%.
Finally, some skills such as Whirl can be maintained with the use of Adrenaline once Stamina is depleted.
Game Pressure's description of the adrenaline point usage may very well be the absolute extent of the purpose for AP, however, some players have explained (somewhat vaguely) their usage in finishing moves.
According to a couple different posts I've read from various forums (Steam being one), adrenaline points can be used by holding down the fast attack or strong attack buttons, causing Geralt to execute different 'finishing moves'. By default, these are the left and right mouse buttons.