Wow - your English is very good! I've added some suggestions where you can make your English a little more natural.

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Disavantages and advantages of having part time job when while* being a student

Having a part time job when being you are a student (two ways to say the same thing) may have both advantages and disadvantages. Generally speaking, students can benefit a lot from having a part time job. Firstly, they can pay a part of their living cost expenses and relieve their parents'** burden. (Firstly, they can help their parents by covering at least some of their living expenses) Secondly, it will help they them feel a sense of indispensable independence as they don't need to rely on anyone for their demand needs. Moreover, having a job before graduating can help students acquire more experiences *** and polish their organizational and multi-tasking skills. On the contrary (On the other hand), there are some disadvantages. First of all there is the lack of time for concentration on study. Students do not have enough time for self-study, research or getting homework done. They can't simultaneously coincidentally focus on both study and work affairs. As a result, If they try to, they will get exhausted and stressed. In conclusion, if you have a part time job , you should have to be good at managing your schedule.

*While denotes a passing of time, so works better with the progressive tense, eg. while being. ('While you are' is also ok as 'you are' indicates time passing.)

'When' denotes a more definite moment in time, or a complete body of time, and so clashes with the progressive tense which indicates passing time.

** Use of '. If the owner of the object noun is plural, the ' goes after the s - Parent's indicates 1 parent. Parents' indicates 2 parents.

*** Experience is normally used in the singular to describe a collection of similar experiences. eg. 'After working at IBM and Microsoft I have lots of computer industry experience'. In a work context, experience is almost always singular. Experiences plural tend to be used for more physical, emotional or spiritual times. eg 'I climbed to the top of the mountain, and then we saw the temple at sunset. They were amazing experiences.'

Great job!

Disavantages and advantages of having part time job when being a student

Having a part time job when being a student may have both advantages and disadvantages. Generally speaking, students can benefit a lot from a part time job. First, they can pay a part of their living cost and relieve their parents'*** burden. Second, it will help them feel a sense of independence as they don't need to rely on anyone for their demand. Moreover, having a job before graduating can help students acquire more experiences and polish their organizational and multi-tasking skills. On the contrary, there are some disadvantages. First of all is the lack of time for concentration on study. Students do not have enough time for self-study, research and getting homework done. They cannot coincidentally focus on both affairs. As a result, they will get exhausted and stressed. In conclusion, if you have a part time job, you should be good at managing a schedule.

*** parent's also works, but this possesive only refers to one parent.  As you're talking about a plural number of students you would probably refer to a plural number of parents.  Makes more sense.