Not quite — the goal is the correctly-sized wire for the load, not simply the thickest one available. Wire is chosen so it can comfortably carry the circuit's current, with allowance for how hot the surroundings are and how many cables run together (derating). A conductor that is too thin runs hot, wastes energy as heat and is genuinely dangerous, so under-sizing is never acceptable.
Going one size thicker than the minimum is often a good idea on long runs, because a larger conductor has less resistance and therefore less voltage drop, so appliances at the far end get their full voltage. That is a real benefit.
But endlessly oversizing every circuit has downsides: it costs more, thick cable is stiff and awkward to terminate neatly in switches and boards, and beyond the size the load needs you gain very little. Just as important, the MCB must match the cable — fitting a bigger breaker to a thin wire to "stop tripping" removes the very protection that keeps the wire safe. The right answer is to size each circuit to its appliance and run length, step up a size for long runs, and match the MCB to the cable.