WhAz Up!!! I'm Paul Lee.
This is all the things you need to know about
how to turn SSJ,SSJ2,SSJ3,SSJ4
This is what i know ... so far
SSJ Advantage: It increase the overall power. Disadantage: None
SSJ2 Advantage: As a SSJ 2, they have the abilty to adjust their strength/speed/agility. More experienced fighters such as Vegeta and Gokou, they know how to balance up to make them well adjusted. If successful, it can also result in increasing more strength/speed/agility. However, the gain isn't as much as from Saiya-Jin to Super Saiya-Jin. Disadvantage: If one part of the power goes up the other two have to go down. For example, if a Saiya-Jin chooses to have more strength, he/she has to sacrifice speed and agailty. Simple as that.
SSJ3 Advantage: As a SSJ 3, all areas including speed, strength and agility are increasd proportionally. Which makes SSJ 3 the most complete transformation available for Saiya-Jins. Disadvantage: Since a SSJ 3 is much more powerful transformation, therefore it uses up more energy too. A SSJ 3 fighter can fight for a while, but he/she gets tired very quickly too. From Gokou's final battle against Majin Buu, we learn that resting will not build up or regain energy, instead it loses energy.
SSJ4 Advantage: It increases the overall strength/speed/agility. Which ultimately makes SSJ 4 greater than SSJ 3. The strength, speed and agility are well balanced out, no need to read adjust them to suit the Saiya-Jin like SSJ 2. Disadvantage: It uses up too much power, just like SSJ 3. This transformation does not last long. After 10 minutes or so, the Saiya-Jin transforms back to a normal Saiya-Jin (Not even a SSJ, but an ordinary Saiya-Jin) I guess the transformation takes too long, unlike the tranformation from a Saiya-Jin to any of the other Super Saiyan Stages (1, 2 or 3).
SUPER SAJINS
GOKU:1,2,3,4
VEGETA:1,2,4
GOHAN:1,2
GOTEN:1
TRUNKS:1