Whether or not to take DMDs is a personal decision and there really is no right answer (although people can get very passionate on both sides of the argument!).
I am a fan of DMDs. One huge reason for this: they work brilliantly for me. The years I have had off DMDs have seen loads of relapses and worsening disability. The years I have had on DMDs stop this almost dead: I had a couple of very minor blips, not worthy of the word relapse, and only one new lesion during more than 3.5 years on Copaxone and I have had only one minor blip on Rebif, when it was too early for it to have properly kicked in, and my lesion count has gone down - this is since June 2011.
So they work wonderfully for me, but they do not work as well for everyone. Thankfully though, these days there are the second line DMDs for people who the injectables don’t work (i.e. Gilenya and Tysabri) - but to get onto one of them, most people have to have tried the injectables first.
I think one of the most telling things about the injectables for me is that, once someone’s been on one for at least six months, neuros generally consider a clinically significant relapse to be a “treatment failure” and want to move them to something else. So, the data may say that the injectables only reduce the frequency of relapses by 30%, but neuros expect 100%. [By clinically significant I mean a relapse that is serious, debilitating or disabling.]
But what about someone whose MS is mild - should they bother? Well, even accounting for my bias in favour of DMDs, yes, I think they should. Two reasons: first, DMDs work best when they are started early and before any serious disability has set in and, second, DMDs are preventative not curative and no one knows when the next relapse (which might have been prevented or at least reduced by a DMD) will be a doozy and leave someone with much worse, permanent disability.
Some of the things that injectable DMDs have been shown to do: reduce the frequency of relapses, reduce the severity of remaining relapses, reduce disability, extend life span, slow progression. Yes, they have side effects, but the vast majority of people only get red blotches and/or a bit of short-lived stinging and “flu” side effects are normally easily managed with paracetamol or ibuprofen and they usually wear off anyway. When I compare those two statements, it’s an easy decision for me.
PS One of the most common reason for not going on a DMD is being scared of needles. The manufacturers have tried to help with this by providing autoinjectors and some of these mean that you don’t even see the needle.