Exceptionally large clumps might be a concern, but I'd also be a bit concerned about predictable patterns or general movements of cards throughout the deck.
I think that can be largely eliminated by using cutting and stripping (sometimes called side shuffling).
- snip -I agree, intuitively it feels like alternating riffle and strip shuffling should solve the problem of any human induced shuffle bias.
On the other hand, there are a lot of things that seem intuitive but which turn out to be counter-intuitive in real life. Any time you put a human being in charge of creating randomness, I become very skeptical. We are very bad at it, and yet in most cases we believe we are very good at it. It's probably possible to find a system of shuffling that would eliminate any bias, but I'm not sure what that system would be or what percentage of people would realize the importance of using the recommended system.