When you create an options pool it has the effect of pricing the shares for future investors as if those option shares existed. Basically, when you create an options pool you dilute all existing shareholders.
If the options pool doesn't get used and you want to cancel it later, no problem... but that has the effect it reducing the total number of shares (including the option pool), which is equivalent to increasing the % equity of every shareholder at that time. Basically, if you create more options than you need, and cancel them later, that has the effect of diluting you (the founders and existing shareholders), and transfering some of your % equity to later investors.
So, our advice is to create only as many options as you think you'll need between now and your next funding round, and if you need more you can create more then.