Buffs are effects that can't do damage but alter the target's stats, be it your own or the enemy's. Some skills create buffs, but they are not buffs themselves.
The passive skills which increase buff effect apply to all visible buffs (but not debuffs or charges) placed on your character - if it brings up one of those little squares in the upper left and it's good for you, then it will be affected. This includes such things as the buffs created by casting blood rage, phase run, and immortal call.
The passive skills which increase buff and debuff duration apply not to buffs on you but to buffs (including debuffs) you create, either on yourself or other entities. This includes all the above as well as such things as the debuffs placed on cursed monsters.
Skills causing buffs/debuffs (affected by both buff duration and skill duration):
- Blood Rage
- All curses
- Explosive Arrow
- Immortal Call
- Infernal Blow (technically, and likely to change - it affects the duration after the hit that they'll explode if they die)
- Lightning Warp
- Molten Shell
- Phase Run
- Poison Arrow (The poison debuff that the cloud puts on monsters)
- Tempest Shield
- Viper Strike
Note that spells which give you frenzy/endurance/power charges are not affected by these.
Inner Force and Buff Effect Passives
The Inner Force Notable Passive grants 15% increased Effect of Buffs on You, when taken together with the other two Buff Effect nodes in its cluster, this results in a 21% bonus.
Basic Passives affecting Buffs are:
- Buff Duration (10%, 15%)
- Buff Effect on You (3%)
The following is an excerpt from the PoE forums about how the "increased Effect of Buffs on You" passives work:
Buffs, in this case, refers to things that show in the top left of the screen, are not charges, and are not bad (those would be debuffs, these passive don't make those worse for you).The list of buffs affected by it is:
- All player aura skills(both your own as well as those received from other players)
- All positive auras from friendly monsters(Spectres from Raise Spectre ability, Dominating Blow monsters]])
- Rejuvenation Totem aura
Skills which make buffs:
- Blood Rage
- Righteous Fire
- Phase Run
- Tempest Shield block buff
- Molten Shell armour buff
- Immortal Call (technically, but being x% more immune is not noticeably different in practice)
The Inner Force and Buff Effect passives increase the bonuses from buffs that affect yourself. It does not increase damage dealt from buffs as it is something that affects enemies.
One has to be therefore careful when amplifying some two-sided effects. For instance, Righteous Fire increases the spell damage bonus from the buff, but also increases the damage dealt to yourself without increasing the damage dealt to enemies. Using Blood Rage increases the lifeleech amount as well as the attack speed on you, but also increases the Chaos Damage degeneration.