In the picture we have Jay Cutler, classic old school bodybuilder. Bodybuilders have to go through different phases in order to gain so much body mass. It is impossible to gain just muscles without gaining any fat (if someone does suspect him of steroid use).
That’s why bodybuilders have a period they call “bulking”. Usually bulking is done in autumn and winter, because obviously you wanna cut for the summer body. While bulking your aim is to gain as much muscles as possible, but you acknowledge that you will put on a layer of fat as well. The weights that are lifted in this period are usually greater than in the cutting phase, and the repetitions are less. What makes bulking easier than cutting is the diet you have to respect with each. While bulking, it is not so important to calculate every calorie you take in, but rather to give your body enough energy to grow, maybe even more sometimes.
In the cutting period what bodybuilders try to achieve is burning down the un-wanted fat that came along with the mass you’ve gained in the bulking period. The cutting period is characterised by dropping down the weights and doing more repetitions, trying to get the muscle to get more ripped and also get rid of more fat than normal. A certain kind of cardio is made while lifting weights in a fast manner, but muscle mass in not lost.
In conclusion, both bulking and cutting are necessary for a great physique, and they should be gone through and respected. If done properly, it is impossible that you do not gain mass and afterwards lose the fat. Lately, more and more people recommend that you start with a cutting session, so you start off with less fat overall. Afterwards go get the mass of the bulk,and then cut down the fat again, to get the desired body.