So in the process of learning how deep/shallow I should get with my trolling motor and depth finder, I've kinda chewed up the blades on the prop that came with my motor. Now they're not broken or anything, but are definitely a bit rough around the edges.  I've been wondering to myself "When should I actually replace this prop? When a blade breaks? When a huge chunk actually comes out? Is it scaring fish? 

Whattya think?

I always keep a spare prop with me and I usually only change props out when one actually breaks.  Just knicked up wont hurt anything.  You could buy a new one and change it out and keep your knicked one for a spare. 

Are there any fractures? or is that the whole extent of the damage?

You definitely do not want to wait to have a blade come off that's bad!!!

If you are in the slightest bit doubtful of this prop being safe to run replace it.

If it truly is just pitted you can have it serviced by a prop shop which is probably what you should do anyway to be on the safe side.

This is the prop on the TM not the outboard right??  On the TM I dont think it matters, but on the outboard it makes a HUGE difference.

Duh!! I should have read it a little closer I think he is asking about the TM. :-[

If it is the trolling prop then a few nicks can be smoothed out with sandpaper (Sorry)

But yes a damaged TM prop does make more noise than a new one and should be addressed

NO ONE is tougher on a trolling motor prop than I am. Mine is in the sand, rocks, logs, and weeds on most trips. What I do is take the nicks and dents out with a file or even some times with an angle grinder. I keep them pretty sharp for cutting weeds. I replace it every couple years when it gets too small. I do carry an old one for a spare in case I destroy a blade on a rock.

Yeah sorry, I shoulda made it a bit more clear.  The little reservoir where I fish I can only take trolling motors (no gas engines), so it's not a huge "safety issue" like it would be with a fast moving outboard or something.  But I see the nicked edges and the rough gouges and I'm wondering how much noise it's making in the water and scaring fish.

TM props with dings and rough edges will create noise due to cavitation (air bubbles) off that leading edge. If the damage is bad enough it may even throw the balance off on the prop and cause a slight wobble making even more noise.

You can re-grind down a rough prop at home but obviously not on the lake. Carry a spare prop for the lake if you damage the prop on the TM. They're usually not hard to change on the water.

File them down smooth. That will get you some more usage and it won't hurt to file on it.