Advantages The user's physical strength, speed, stamina, and durability drastically increases.
The user's ninjutsu, genjutsu, and taijutsu become very powerful.
The user can harness the natural energy surrounding them, turning it into an extension of their body, and increasing the reach of their attacks.
The user gains the ability to sense chakra around them.
The user does not feel as much pain, and recovers faster from physical damage.
[edit] Weaknesses If the user draws in too much natural energy in the attempt to initiate Sage Mode, they run the risk of transforming into a toad, then into stone.
In order to gather enough natural energy to initiate the transformation into Sage Mode, the user must remain perfectly still. Because of that, the user can be an easy target for an opponent.
Because the user needs to move during combat, the Sage chakra cannot be replenished, which means the user can't stay within this state for extended periods of time.
The two weaknesses mentioned above can be bypassed through the Sage Art: Amphibian Technique, where one Sage gathers chakra for another or as in Naruto's case, shadow clones can be used for the same purpose.
After Sage Mode has ended, the user appears to experience exhaustion.