I think they do. In a company where the booking/writing is good, they don't matter as much because guys can be heated back up again if it's done correctly. Look at Brock Lesnar. He lost to HHH at Mania two years ago and no one even remembers it and he's an unbeatable monster in all of six matches (off the top of my head). Then on the other hand is a guy like Ryback, who is also is not as talented, obviously, and thus needed more help after his loss - and didn't get it. He has gotten over in the mid-card now, and hopefully will get pushed again (because I love the guy), but it was a long road for him.
My opinion on this is a big part of why I am of the opinion that Reigns should win tonight. I think he'd be even more fucked than he already is, and the whole point of Brock laying waste to Cena and ending the streak, and Reigns beating Bryan and winning the Rumble, was for him to win. If the creative hadn't failed him so miserably along the way, the option of him losing would be there, but it is what it is.
So... Yes they do matter, especially to guys who are trying to get over, like Steve said.