It seems fairly safe to say that N always viewed these organizations as temporary, intended for emergencies to fill transitory gaps and to be dissolved or merged with the "home" regiments as soon as the operational situation permitted--Drouet d'Erlon's 9e Corps in 1810-11 in Spain/Portugal is but one example of this phenomenon. In some cases, these measures, intended as temporary, took on an extended existence owing to operational exigencies and, in some cases, the anomaly was resolved by forming them into new regiments when other, preferred options did not seem feasible. N was very conscious of regimental identity and endeavored to preserve/foster it as much as possible (the construction of the Army of Germany in 1809 as recorded in Saski's first two volumes provides a good example, but there are many others). Some suggest that economy was also the reason behind the creation of very large regiments with six or even more battalions as this was less expensive than building new regiments.
It is useful to note that the resort to temporary, provisional units was a common practice across Europe in emergencies (many of Wittgenstein's units in 1812 or Bavarians in 1809, for instance), but most armies, like the French, attempted to unite men with their home units as soon as they could.