Sassoon's poem has a pretty vague title, "Does it Matter?" Does what matter, Siegfried? He could be talking about, well, anything: Does the color of your car matter? Does the pattern of clouds in the sky matter? Does the fact that your parents, in all likelihood, dropped your on your head at least once when you were a baby matter?
Maybe, maybe not. But that's clearly not what Sassoon's after here. In fact, if you've ever read any Sassoon, you can probably guess what he's asking about: war. And World War I, specifically.
In the most general sense, then, the poem's title seems to be asking whether the reasons we go to war matter. However, once we start reading the poem we realize the speaker is asking the question from a much more jaded perspective. He wonders, for example, if the loss of one's legs, sight, and dreams really matters?
It might sound like the speaker's saying that they—to be blunt—don't. But is that really all there is to it? Probably not. We think the speaker's using a healthy dose of irony and sarcasm to prove the exact opposite and to answer his own question: it does matter if you get wounded, both physically and psychologically, in a war. It matters a lot.
And according to our speaker, anyone who thinks differently is pretty much a jerk.