Spreadproof did a good job of explaining it, but there are a few things worth mentioning. My investment plays are indeed the heaviest plays, and the amounts mentioned were accurate. But I am not so sure that I am done with the Investment plays for the season just yet. You never know when an opportunity will present itself! If a line, warrants an Investment play I will not hesitate to place the wager. With that being said, lines are tighter than ever, so how much opportunity remains is yet to be seen. Just have to play it by ear. Action plays are bet for heavier amounts than those mentioned. Only, when I first began to wager these plays, many years back, were they bet for those amounts. Early on in the season I was flat betting my action plays for $350 per play. Now these plays are bet a bit heavier late in the season, and they are no longer being flat bet. Small plays, are simply my response to the occasional slump. I use them to break through a bad stretch, with as much damage control as possible, and minimal losses. I also use these small plays for lines, that are different than the ones I have for the game, and therefore have me showing some value. More specifically for the lines that I show some value, but the rest of my capping contradicts the play. For example the other night, Jazz/Nuggets, I had Jazz -5 for myline, and the actual line was Jazz -9. Significant value, in terms of the line difference. But every tool I use to cap, pointed toward the Jazz winning big. So I decided to bet the Nuggets +9 very small. Jazz win by 7, I win my bet, but clearly no significant edge there. My way, basically, of betting a game, so that I do not look back at the game, at the end of the day, and say "I should have bet that game."
When I designate a given play, as small, action, or investment, what I hope to convey is the relative strength of the play, and not necessarily the dollar amount that should be bet. That should be something left in the hands of each individual to decide. What would help, in deciding the amount for each person is this: Ask yourself this question, "If I were betting a sport, and I had three different plays. One being the smallest, One being the heaviest, and the other being somewhere in the middle, and I was determining which to bet based on relative confidence, what fixed amounts would I decide to assign to each type of play?" This of course will depend upon your bankroll, which is why I prefer each person answer this question for themselves. Betting at your level is extremely important. For some, it may be wise to bet 1 unit on small plays, 3 units on action plays, and 7 units on investment plays. For others, it may be preferable to bet 1, 5, and 10 units respectively. For yet another group of bettors, it may be best to bet 1 unit on small plays, 2 units on action plays, and 3 units on Investment plays. It is simply a matter of preference, and a decision that should be made based on the situation of each person's specific bankroll. Like I said, when I designate a play as small, action, and investment, what I really hope to convey, is the relative strength of the play, and not necessarily the specific amount you should bet on each. That is up to you to decide. I hope this helps.
Also thanks to spreadproof, for taking the time to explain..