I've heard/read this many times. Something a long the liines of "he's a got a pair and FD, that's a monster in NLHE, he's shoving" blablabla.

Well... if you get Pair + FD on the flop is it always a shove? When is it not a shave? Does it matter what pair you have? Top, middle, bottom? Overpair? Pocket pair? What about stack sizes? Villain(s)? Fold equity? Are you drawing to the nut or near nut flush or some baby flush? Etc.

Completely unclear about this.

With a short stack you probably got to shove. With a deep/big stack you are in deep trouble.

Why not get yourself the Harrington on Cash Games and clear up what is unclear now about your game. You may even become a winning player after studying the books (vol 1&2)

No, and it's often a bad idea to shove.

pair+fd is considered a monster because it usually has 14 outs to improve, and 14 outs on the flop is a slight favorite over one pair. You're not exactly happy to get the money in but it's a semi-bluff -- most of the time your opponent is unable to call a raise with the hands you are flipping with and he just forfeits his 50% of equity.

Some examples of times when it may be bad to just shovel all the money in:

1. you have top pair meh kicker + flush draw. In which case you only have 12 outs at best (because villain has top pair better kicker or better).

Board: Ac 7s 6s
Dead:

equity win tie pots won pots tied
Hand 0: 44.545% 43.94% 00.61% 435 6.00 { As2s }
Hand 1: 55.455% 54.85% 00.61% 543 6.00 { AhKd }

2. you are very deep and villain's range for stacking off is only 2p+ which you are an underdog to, and would be much better off just calling.

Board: As Ts 9h
Dead:

equity win tie pots won pots tied
Hand 0: 36.970% 36.93% 00.04% 10236 12.00 { 9s8s }
Hand 1: 63.030% 62.99% 00.04% 17460 12.00 { AA, TT-99, ATs-A9s, T9s, ATo-A9o, T9o }

3. you are multiway and unlikely to fold out a better draw -- pair+fd only has such good equity because it is impossible for one player to have both a better pair and better draw. But two players can combine to crush you.

Board: 9h 4s 3s
Dead:

equity win tie pots won pots tied
Hand 0: 15.725% 15.73% 00.00% 142 0.00 { 9s8s }
Hand 1: 43.411% 43.41% 00.00% 392 0.00 { KcKh }
Hand 2: 40.864% 40.86% 00.00% 369 0.00 { As7s }