I’ll echo what others have said about this tool: it’s not an absolute necessity, but it can be really useful.
For me it really shines when setting really old front derailleur cables that don’t have barrel adjusters. The tool allows finer control during initial tensioning than using a pair of pliers. Old pro wrenches will scoff and say it can be done without this tool. And they’re right. But any tool that makes a job easier means the job goes faster which means you’re out on the road/trail faster, too.
If you’re just getting into cabling your bike yourself, invest in a good set of cutters first. This tool can come later.