So as someone who is famous for playing Nurgle, what is this Tzeentch model doing in my miniature collection? Well I was originally an Ork player. I had a Space Ork army and a fantasy Ork and Goblin army before I had a Nurgle Chaos Space Marine army. When the second edition of 40K came out, Orks could have Chaos allies so I converted the space marines that came with the boxset to chaos and started using them.
Although I was never short on rank and file troops what my army needed in this era of character dominated games was something that could compete against all the assassins and inquisitor lords that my "friends" fielded against me. I swear I never won a single game of 40K with my Space Ork army under the Rogue Trader era rules. I did a little better in second edition but Eldar were clearly superior until a few revisions were added to the game. It wasn't until third edition that characters were neutered and the game became fairer with less domination by Marines and Eldar. There are still opportunities to abuse an army list and the Eldar still attract some of the least enjoyable people to play against. Check out the fourth game I played at the 2003 Vancouver Grand Tournament for an example.
This model shows my clean and bright style but it doesn't have enough highlights or lowlights. It is painted so cleanly that I could quickly make it look a lot cooler. I discovered I could add highlights but the sealent I used back then does not allow washes to still work so if you want to add more lowlights to old models you must paint them on. I eventually painted a new Chaos Lord or Chaos Sorceror on Disc of Tzeentch as I don't think lesser heroes can have them. The rules keep changing so who knows, I don't have time to read all the rules or keep up with the meta game.