In reply to Jack Geldard - Editor - UKC: I think bouldering is a great way to build strength (short problems - good for crux moves) and power endurance (longer problems/traverses - good for longer crux sections).
It's rare that I can really 'train' leading trad routes. I can't max-out repeatedly to gain fitness in the same way as I can bouldering.
On a less technical level bouldering is great for building up your 'repertoire of moves', trying new things, gaining confidence on rock types and practising
trying very hard (which is a difficult skill to master).
On a mental level (which is just as important as a physical level) bouldering is great because you gain lots of experience and familiarity with the rock, and you might climb much harder technical grades than you are aiming for on a trad lead - hence building a mental buffer zone, knowing you've climbed 5c earlier in the week, when the route you're attempting is 5b.
So advice from me - bouldering is good for your trad at E1 level.
Nice article TRNovice.
Jack