Ref your question regarding controlled airspace.
I suppose knowing your flight conditions is important then. The reason is that ATC have a duty to 'give instructions to aircraft to help prevent collisions in the air' (as the MATS would have it). In Class D airspace (which covers most airports) we are required to separate IFR traffic from IFR traffic, but only to pass traffic info to IFR on VFR or to VFR on VFR. Therefore our ability to prevent collisions etc relies upon you remaining VMC so you don't bump into someone. Out in Class G if you want to go IMC when you're supposed to be VFR and then find a cloud with a plane in it then that's your lookout (or it isn't, you might say!!).
'Remain VMC in the zone' is therefore your life preserver, and I'm sure your instructor has told you that if in complying with an ATC clearance you are unable to maintain VMC, tell them and get the clearance changed!!
Good luck!
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"Take-off is optional, Landing is mandatory"