Well, I like the analogy of the brain being an attic; but I prefer to think of it like a Tardis - bigger on the inside.
I Don't know if I'm a craftsman or not - but think that if you know your craft - and that's great! - but you only know your craft, you're missing out on so much.
It's ok to know a little about a lot.
It's ok to be a car mechanic who is also interesting in shakespearean plays and also likes to cook.
It's completely normal to be interested in things other than your chosen "craft".
People who out-of-the-box think, can do so because they haven't limited their "tools" to the ones associated with their "craft".
I don't think there's a limit to knowledge.
Holding on to useless fact may or may not "take up space" but knowledge isn't simply fact - it's understanding and often, facts are just a stepping stone to understanding.

Facts are not discrete, unitary objects. Once you know two things it is often possible to deduce a third, Knowledge is a cascading process, not a library of things known.

This is a rather antiquated analogy that doesn't really hold up very well. Though he studied medicine, A. C. Doyle was not a cognitive scientist, but a fiction writer who wrote this back in 1887. Cognitive Interference Theory provides a better explanation of forgetfulness.

[en.wikipedia.org]

The analogy is a bit reductive, and, i think, inaccurate.

I feel this depends quite heavily on what the man is goal is. If his goal is the Mastery of a very specific trade, such as Holmes, it may very well be true. But if his goal is a rich and fulfilling life, or a deeper understanding of the universe, then it may be that there are very few facts which are truly unworthy of notice. All things are interrelated after all. However, as we have a very limited amount of time in which to learn things, it would make sense to spend it studying foundational facts, rather than day to day gossip. Just foundational facts from across a wide range.