Don't get me started about more than one sewing machine... I only had one machine (a Singer from high school until 30 years ago) but I was only sewing clothes then. When it stopped working I took it to be repaired and found out I had totally worn out the the machine so I bought a simple Viking 150 (still just sewing). When my Mom passed away in 2000 she left me a note to buy a really good machine with some of my inheritance so I did. Got a Viking Designer 1 and I love it. But that started it, as I started quilting, when that D1 got older I was so afraid of it breaking and I started taking quilting classes so I bought a Featherweight (the type of machine I got in middle school when I started sewing) for classes. Love it but I think I went crazy, bought a Viking 183 for class also. This year I wanted a bigger throat for free motion so I got a Viking 875 with 10 inch throat and within 1 month bought a Janome 8200 with an 11 inch throat.
You really need more than one for all the reasons mentioned by others but be careful it can become an addiction. Guess we all have to have our obsessions. I do think it's important to have a machine to take to classes if you attend with any regularity, but be careful. I have a quilting friend that has 13 machines, some older ones for display as she has an actual quilting room but each machine has different features....Oops I also have a Viking surger....Love them all