You can *generally* get away without until you have carbon components. After that they become essential. Carbon gives no warning, you nip it up, all seems OK, right I'll just check that...crunch.I don't think you really need one do you unless carbon is involved?
(and then I seem to recall that it's a good idea to invest in a special hammer as well)
https://www.wiggle.co.uk/topeak-combo-torq-wrench
I have one of these, which for the price takes some beating for its range of both allen head size and torque range. you essentially gauge torque by eye from the pointer on the scale. accurate enough for bike maintenance
I only got one to use on my GXP crankset - the leverage is great for extracting the cranks with a hex.
Noo - using a torque wrench as a breaker bar is a sure way to knack it.