Since this is the internet and you really don't know me from anyone, I will post the standard go / no-go gauges are always a good to have when assembling your own rifle. If you plan on assembling your own uppers (and I mean multiple uppers), then the gauges are good to have.
Now that's over...
When I've purchased a complete upper from a reputable manufacturer who has been in business a few years and is a stable business that won't go out of business overnight, I don't feel the need personally to use go no-go gauges.
When I assemble an upper myself, I'll use go/no-go gauges just to be 100% sure. As long as I purchased quality parts from reputable manufacturers, I've never had issues. The AR-15 is built upon standardized dimensions. The barrel keys into the upper. The barrel nut gets torqued. Compared to building other rifles, the AR-15 is a comparative pleasure.
As a contrast, assembling an AK-47 from a flat is a comparative pain. Aside from rivets, pressing in the barrel into the trunnion, absolute necessity of checking headspace with a go / no go / field gauge is a must. Under supervision, I've done it one time. I don't ever want to do it again. Buying a surplus mosin, go / no go gauges are important.
Not sure if this helps.