In relation to the Coldsteam Guards and indeed all of the Household Division, every single ceremonial soldier is also an active soldier, meaning that they all have the capability to serve internationally or however the monarch deems fit (this in practise is controlled by professional senior officers). Guards by definition are not regiments of the line, they are protectors of the Crown, however will often be tasked with line infantry work nonetheless. This is especially prevalent after the Napoleonic Wars, where Guards gained fame for their successes in the Peninsular War and in the Battle of Waterloo (and surrounding battles).

In terms of their skill and aptitude, older regiments of the British Army are often percieved by some authors to be 'better' due to the way the regimental system works. A soldier's alleigance to "the colours" is one of the attributing factors towards older regiments fighting better. This book by Allan Mallinson details the intrigues of the British regimental system.

One of the best examples for the Guards in the Second World War is obviously the Guards Armoured Division, which played a role in the Normandy campaign in 1944, and then the liberation of Europe. It led XXX corps in Operation Market Garden in Holland to try and relieve airborne troops. The Guards Armoured Division also liberated Brussels.

In terms of recruiting, the Guards division (known as the Brigade of Guards until 1968) ran their own recruitment process for officers up until the mid 1990's. There was not exponential demand for Guards; the Irish Guards for instance only raised one extra Battalion (the Holding Battalion, later known as 3rd Battalion). British Troops of the Line in the Second World War had less of a role to play than Britain's unconvential, innovative ideas; the commandos for example, as well as the LRDG and SAS in North Africa.

Edit: Spelling