If you want to shoot in tournaments, you'll probably find that the maximum and minimum bow length is defined in the regulations. In general, you'll get slightly better accuracy from a longer bow, provided you have the muscular strength to hold the additional mass steady. This is because the velocity of the arrow will build up slightly more slowly for the same draw weight. In addition, with a very short bow, the angle that the string will make at full draw will be so acute that it will be difficult to hold steady and not pinch the arrow. A recurve bow will of course normally be longer than a compound bow, so you must decide what the purpose is for the bow. For example, a shorter bow is easier to manage in among trees etc., if you are hunting, but it may not fit in other ways.
You can only vary your draw length by a small amount. You need to ensure that you get a bow that is compatible with the length you want to draw. You will get maximum draw length if you hold your bow arm right out straight, and draw the bowstring right back to your ear. You will get the minimum draw if you bend your bow arm slightly, and draw back to your chin. Many people assume that a longer draw length is better, however this assumption is wrong. Why? Well, even though a longer draw will transfer more energy to the arrow, and therefore create a flatter and more stable trajectory, you can only capitalize on this improvement in trajectory if you are a very competent archer, or a machine. There are two reasons for this. First, if your draw is longer, the arrow is in contact with the string for a longer time, which means that deviations in the side-to-side movement of the string have longer to affect the trajectory. Second, you'll find it harder to achieve a consistent 'anchor point' if you pull the string back much further than your chin. Small variations in where you hold the string at full draw have enormous effects on where the arrow ends up. Most expert recurve archers only draw to their chins.
You say that is all very interesting, but my QUESTION is: How do I determine my draw length? ANSWER: The easiest way to measure draw length is to nock an old arrow in your bow. Draw your bow back to a full, comfortable draw, and have someone mark the arrow at the point where it meets the back (target side) of your arrow shelf. Carefully let your bow down. Measure from the base of the groove of the arrow nock to the place on the shaft that you previously marked. This is your draw length. Add 1 " to that measurement and that is your arrow length. This additional 1 " will give you proper broadhead clearance.
For compound archery, the chin often does not make a good anchor point. The reason for this is that, because the bow will be quite short, the string will make a very acute angle at the nock point. So even though you'll be able to touch the string to your chin, you won't be able to touch your nose or lips, so you won't be able to get as consistent a draw length. Consequently, most expert compound archers draw the string back to the angle of the jawbone, and let the string touch the nose higher up. Most modern compound bows have a set draw length determined by settings on the cam. A set draw length makes it easy to get a consistent draw every time. In this case, a release aid is normally used with a D-Loop on the string to make this easy, plus a release aid along with the D-Loop almost completely eliminates the archers paradox. Please see your owner's manual for specific settings and adjustments. If you are not well versed in these adjustments, it is better to have a professional do them for you.
In summary, don't assume that you should buy a bow suitable for a 31-inch draw when your draw is only 29 inches, and hope that you'll work up to the longer draw. You probably can, but it might not be for the best in the long term.