Given how out-of-it, how spaced a lot of Low songs (especially early ones) sound, it says something about "Lazy" that Alan wrote "always wanted to hear a cool echo-y dub mix of this song" on the old Low song backgrounds page. He also notes that although his sister's name is Sarah, "it would be mean to say it's about her."
The bass and drums sound fairly standard but Alan's guitar has a shimmering, underwater feel that manages to not approach the Durutti Column's sound (the standard for that kind of guitar effect), and is due to a weird vibrato Alan got from an old amp (one he doesn't have any more). It's interesting to think what he could make of this sound, if he was still interested in that kind of effect. The band's sound seems to be moving away from the creepy indeterminacy of the early years to something more definite, more sharply defined (even on ostensibly foggy or distorted songs like "Take Your Time"). Low used to be more reticent, used to keep their cards closer to their chest.
"Lazy"'s lyrics only enhance that; aside from the refrain of "Sarah, Sarah you're lazy" there's just near-constant repetitions of the sentiment that "it's not enough, there's not enough for two." Alan's coy half-demurral makes me think that "Lazy" is a teasing glimpse back into the selfish ways of kids, not just his sister's but his own as well. Who with siblings hasn't realised as they grow up that you didn't need what you used to think you needed? "She says it's not enough for two," but so does Alan. They're both lazy, and while the aqueous atmosphere of "Lazy" suggests that may be because of humidity as much as anything, hindsight suggests they're also too lazy to make a productive compromise instead of haggling over what is probably, when you get right down to it, enough for two.