Big Growlithe, low IV, worth the 50 candy?
Answers
Or if you consider the fact he has enough candy to power up a level 1 Growlithe all the way to 40 and evolve it, paying 50 candies and 0 dust for a usable Arcanine is definitely worth the investment.
Weak IV pokemon that are also low level are not worth investing in because they cost stardust which is the resource that limits players. This Growlithe is already level 29 so he can simply choose to not invest any stardust in it and still have it be useful.
If he has that many Growlithe candies they probably aren't rare in his area so 50 candies is almost nothing to him.
Definitely worth it: I've evolved 4 with good IVs and always got imperfect move sets. With the current Gym game, having maximum CP is less important than it was, because its so hard to hold gyms anyway, and its even easier than it was to beat them down. So with the right moves, its worth keeping. But since its already at level 29 (or 30 maybe?) I probably wouldn't bother powering it up further.