When to chase a gutshot....
You should take into consideration the read you have first. Does villain have a big hand? Based on his preflop and flop actions, will you get paid off if you hit? Is he just C-bet bluffing
If you think he may not be that strong, perhaps a raise with the gutter-ball would be in order. However, if you feel villain never folds, there is no point in raising.
Also, consider board texture. Ideal spots are when the board is rainbow, and your gutter-ball is to the nuts (I know title does say this, but just to be sure, here it is). Don't chase a gutterball multi-way, if it's not to the nuts. Your gutter could hit someone else too.
Another consideration would be the action pending on current street (flop, let's just say). You probably shouldn't be calling it off with villains behind you that haven't acted yet. You can get into a tough spot if someone raises, and you would be forced to fold (terrible) or call (even more terrible).
So, to sum up:
- Heads up or last to call postflop
- Rainbow board
- Gutter to the nuts (other gutters perhaps HU if villain has a narrow range, that a gutter will certainly beat)
- Great implied odds; villain is strong, and both of you are deep.
Places not to chase gutter:
- Multiple villains behind you
- Multi-way with flush draw on board
- Monotone boards
- Paired boards - proceed with extreme caution (or not at all).
- Poor implied odds, villain or you have too few chips
And last, but certainly not least....
Realize that gutter-balls are pretty tough to hit. 4 outs, like 9% +/- if you see one more card.
Implied odds should certainly be well over 10x to make it profitable. Say like 15x+ inplied odds, and that is assuming villain is going to stack off.
That is all I have to say. If anyone else has other things to add, please do so.