Here at whaacked.com1 the wheel has certainly been reinvented. Instead of choosing the sane option of using Wordpress or another blogging platform,2 I have taken upon myself to write the code for my own website. This gives me a lot of freedom, but implementing the simplest of features are just yet another thing i have to do.
In general, it is quite a bad idea to reinvent the wheel. You are wasting your time and money and your customers time and money. Are you trying to figure out how to rip youtube videos - because you don't even know that youtube-dl exists? Have you built an app whose purpose can be undermined by having the same end goals be accomplished via emails or a shared chat channel?
Reinventing the wheel is a massive time sink, so if you plan to do it it should probably be for the learning experience. Also, don't rewrite your code from scratch. Shoutout to Joel.