You can do quite a lot of things with software synthesizers and other audio software, i.e. you can export a song in almost no time (depending on the amount of things you have to process) without having to record it and set up everything properly, like volume and EQ levels, but you are limited to what your computer can process. If your computer is kinda slow and you want to use a software synth that literally eats your cpu, it's just pain. Hardware has the disadvantage that you mostly have to adjust all the levels on your own and wire up everything properly, but it also has the advantage that you have a real keyboard instead of virtual keys on your computer keyboard or screen. Also the hardware is dedicated to making these sounds, and sometimes hardware also has their own sound processing technology. Some hardware, especially analog synths, can't just be emulated on a computer, like the TB-303. Emulation comes really close to the hardware sound nowadays, but there were still some components making the sound that simply can't be emulated that easily.