This is a popular question in sewing groups we moderate. The real answer is no, you do not Need a serger. However, learning to use one and then buying one, will change your sewing-life.
Some folks think using a serger is scarey or too complicated, but it is not if you take the time to learn to use it properly as it was intended for garment construction.
Most domestic models of sergers at the lower price end of the market are great machines for garment construction. Where the problems come up are when folks try to use them for heavy thick layers to make diapers, inserts and nursuing pads, or heavy canvas and denim totes and purses.
Use the right tool for the right job.
Most all entry level mechanical sergers are well made and not that difficult to learn to use, with one exception, a popular entry-level model of Singer serger is not very easy to keep adjusted for regular garment serging and it results in a lot of user complaints and product returns for this reason.
Do your homework! Be sure to read our article on Buying A Serger and check the Serger reviews on Amazon (they are the largest seller of sergers worlwide) or SewingPatternReview for any model you are consideing purchasing.