What about "request traffic". This phrase is in widespread use by IFR pilots across Australia. IT IS COMPLETELY UNNECESSARY to "request traffic". Centre will always give it to you at the appropriate times. ALWAYS.
ABSOLUTELY NOT, NO WAY!
Traffic is NOT always given, particularly VFR traffic which is often far more danger than IFR traffic, specifically with unverified transponder levels.
I don't know how many times I've heard someone ask for traffic and they reply with, "no observed IFR (emphasis on IFR)" but when asked for VFR traffic, there could be half a dozen nearby.
Why on earth do pilots think they have to request traffic? Maybe because they hear so many others doing it.
The controller isn't in your aircraft. Smoke haze, pollution, visibility, sun glare, rain, the list goes on... have done it a few times under VFR when appropriate.