Everyone is different, but personally...
Over the last 28 years I've been using steroids, one thing I've definitely learned is that I can run cycles without Test and still gain plenty of muscle. When I started using steroids in 1992, I sometimes did Deca only cycles at 400mg per week and gained muscle and strength. Later, I did a Tren and Anadrol cycle and gained plenty of muscle and lost fat.
But although I could build muscle with those cycles, I had no libido at all. Looking at a sexy woman was just like looking at a street sign or a piece of furniture, it registered nothing in my brain and I didn't desire sex at all. Even masturbating to try to get to sleep at night was just flopping a wet noodle around, no desire and no erection at all.
But as soon as I added even a little Test...bang! I had a great libido, erections, and wanted to fuck every sexy woman I saw. On Test and Tren or Test and Masteron, even the ugly women looked sexy as hell LOL.
So for me personally, Test is necessary if I want to have a libido along with building muscle. Which is the point, of course. I got into bodybuilding in large part because I wanted the girls and the glory. If you can't have both, you may have success in bodybuilding, but that's a pretty empty existence. Sex is or should be important to all of us. If it wasn't important to our parents, we wouldn't be here.
Just my own opinion and experiences, everyone is different and has to find what works for them.