I hear this all the time and in the whole realm of work we do in commercial and industrial facilities there are way more important connections we make than tightening EMT connectors (NOT DOWN PLAYING THIS). IN A COMMERCIAL facility, with metal studs, metal ducts, rebar, steel joist, EMT, metal piping for water there are multiple ground path in fact test show (test we make regularly) it is IMPOSSIBLE not to have multiple ground paths. I am more concerned that my guys make that 34.5 KV termination right, or bolt 4000 amp bus properly if they cannot get an EMT connector tight I DO NOT WANT OR NEED THEM IN MY EMPLOYMENT.
As for a DIYer, I feel as I stated if they cannot properly tighten a connector, coupling or locknut they should not be doing DIY projects. In fact I would bet being a DIY'er they will over tighten the connector, coupling...........
And as Jim stated NO IT CAN'T hurt, I just feel the arguments utilized to defend this practice are bogus. Much like the arguments for ground up/down, tape wire nuts don't tape wire nuts and a slew of others electricians make with no hard data to back their argument.
Having said all this 99% of the jobs we do spec EGC's in conduit, you pay me I'll install it.