When the only tool available is a hammer, every problem starts to look like a nail.
Multi-tools are great, they save a lot of time running out to the truck, or running out to the shop, etc. for small jobs, or if you're seperated from your tools for any reason. We can't go through life lugging around a machine shop.
But until they make a multitool with an arc welder, table saw, rollaway cabinet, air compressor, torque wrench, chainsaw, dremel, etc. it's just a nifty pocket gadget.
You can't have too many tools, I have tools I use only once a year, tools I don't really need, but might someday.
When you need a peavey, or a wrecking bar, or a milling machine, a swiss army knife won't do.
I guess it depends on you lifestyle, an apartment renter who drives a new car and works at a desk may get by without any tools at all, poor saps.