Why should I file taxes?

Um...because the law requires that you do so; and to qualify for stimulus payments, EITC, and other Federal or State tax credits.

And you need to see if the tax withholding from your pay covers the actual tax due on your income.  So you might get a refund if they took out too much or you will have a Tax Due if you didn't have enough withholding taken out.  The withholding in W2 box 2 is just an estimate.  You only get a refund from W2 box 2.  Boxes 4 & 6 for SS & Medicare are mandatory taxes you don't get back.  

Do you need to file a return?
https://ttlc.intuit.com/community/filing-and-paying-taxes/help/do-i-need-to-file-a-federal-return-this-year/00/25546

IRS Do I need to file? Interactive tool
https://www.irs.gov/help/ita/do-i-need-to-file-a-tax-return

And see IRS publication 501 Table 1 page 2
https://www.irs.gov/pub/irs-pdf/p501.pdf

if you have overpaid your taxes you won't get a refund unless you file.  if you owe and don't pay, the IRS has the power to garnish your wages, levy your bank account and put liens on assets you own