Isn't the 24-70 much heavier than the 24-105? The gain in crispness seems marginal for more weight.
A zoom is necessary for travel, editorial, street people and often landscape. Not only changing primes in those conditions easily entails dust but it also slows you down critically in situations where the moment might be short. A heavy zoom might be a burden here.
When the situation is staged and under control, like in studio, it's far better to work with primes, since their quality can't be beaten by zooms, at a fraction of the price. posted in Field test between three Canon 24 mm lens on the new Canon 5dMkII