If one wants to maximise 'versatility' ('future proofing'?), there's no reason why one can't do 'both' (and I often do these days) - i.e. 'loop at rose' AND ALSO run a neutral from rose to switches.
A major advantage of loop at switch over loop at rose comes when someone wants to replace the rose with a fancy fitting. Many fittings are much easier to wire with only a single cable, and metal class 2 fittings may make it essentially impossible to maintain their class 2 status in the face of multiple cables.
Well, its obvious. If you want to plug the same load into the sockets. (for example a kitchen). Then a radial will either need to be 4 or 6mm
And as an the op is more of a DIYer, its a bit silly to have to buy one real of 4mm when you can use 2.5mm on a ring.
I'm sure you investigated 4mm prices in the past, and they weren't good value either, as not a common use
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