When you first get it you will think:
"Wow, he suxx"
Then you lvl it up some, and when the wolf is like 2-5 lvls under the mobs lvl you think:
"It doesnt get so much better, but now it doesnt die anyways... Still it Suxx!"
Then when the wolf is at mobs lvl/your lvl:
"WOW! That mob that took me 3 hits now only takes 2 hits!!! Grinding go soo much faster!!"
This is for STR chars at least

If you can make it trough the first 2 steps your gonna be happy, but many sell their wolfs before that...