I definitely have a backup. My main machine is a flat-bed Pfaff 1216 (very similar to the coveted 1222) and my backup machine is a portable Pfaff 1047. Both are late 70's early 80's era all-metal, made in germany workhorses. The flatbed is my main machine because of the built in cabinet and also because it has IDT (built-in walking foot). But I do use the other one when the 1216 is in for servicing. I also use it for sewing knit tops and bathing suits because it has better stretch stitches than my 1216.
Backup machine definitely a necessity if you can afford it!