then it would be natural to plan EVERY flight with the IFR option, as in the UK (can go IFR anytime in Class G without a clearance, etc) it takes zero extra effort.
Well, there are good reasons for planning flights that can be conducted under VFR but not under IFR.
... where icing may be an issue in cloud
... where there are no suitable navaids (OK, that's dying as an excuse
)
... where the destination has no IAP and a letdown is of higher risk than a VFR flight
I'm not suggesting that you shouldn't plan by preference to obey the IFR regardless of conditions, but there may be some circumstances in which the decision to enter IMC requires more than just an "ooh look, a cloud..."