It depends on what you mean by necessary. Is it necessary to spend a ton of money? Certainly not. Is it necessary to have a reliable instrument that inspires you, feels great, and has all the options you care about? I would say absolutely. Sometimes you have to spend a lot to get all those things. Sometimes you don't. My favorite bass of all time (heavily modified over the years) is my Japanese Jaguar Bass that turned 10 this year. It originally cost me $700 or so. I have been satisfied for 10 years.