I do a lot of extreme sports, biketrials riding in particular, which requires strength, stamina and precision. I've found recently that starting weight training has helped make riding easier so i'm well chuffed about that.
Theres always the plus of having a better physique, nobody can say they don't do it to boost their appearance and don't like looking more toned or defined. Its human nature to improve yourself, why deny it?
It also adds a bit of stability to my life. In a life where i'm at uni, going riding, going drinking, seeing friends, sleeping etc. Its nice to have something constant to keep myself remotely in balance.
I'm also 6'5" and Sometimes have back pains etc, i find doing weights strengthens the muscles in my back considerably and since starting i havn't had much pain at all.... in fact i don't remember having ANY.