I had 2 hunters so I could spam raids. When I hit 30 on my hunter I made a warlock. It's currently 26.

Gives you more chances for gear on one class. I did it for my titan and hit a pretty lucky streak on warlock and hunter.

I have one of each and I used my Titan to level up all 3. I got to 28 with my Titan and felt stuck so I started a warlock, when I hit 20 with the warlock I went back to my Titan and played the tiger strike playlist. I took all the engrams I received and put them in the vault. I then switched back to my warlock to cash in and hit 24 in no time. As my warlocks cryptarc level raised I began getting legendaries and I hit 28 with my warlock in almost no time at all. I'm currently doing the same with my hunter but can't seem to get any legendary boots :(

My main is a Titan but I made a warlock, because they are pretty epic to float around as flinging purple death artillery :) but my third is another Titan, hunters are too slinky and light for my tastes. Having more than one of the same class doubles or triples your chance of good drops from nightfalls, raids etc so well worth it, plus once you get them to 20 just vault your gear and use it for your new character, so lvl 29 can be enjoyed across all of them without having to lvl up three of each armour piece :)