That's it!
Keep in mind that not all founders are this savvy when it comes to deal terms, and most investors will push founders to issue a larger option pool than needed. The investor will say something like "we want to be sure we have enough options available to recruit the best employees" or "we don't want to have to issue more options later because it would be a distraction". Both of these arguments have a kernel of truth in them, but they're not very good. You can always issue more options later and it's quite simple. What they're actually saying is, "I don't want you to come back and dilute me later when you could dilute yourself now instead". How thoughtful!
In a perfect world, this would have no effect on you. In the real world, it sometimes causes people to create option pools that are too big/small, since it's a confusing topic and it can be really hard to predict exactly what you need in advance! How people then act in those situations differs massively, but only affects things on the margin (e.g. perhaps the founder will issue a slightly more generous equity package to a new employee because "I have this whole option pool to spend").
tl:dr; this should have very little effect on you as an employee, but if your company's option pool came out of the pre, then the founders probably wasted valuable time and energy figuring this out with an investor who shouldn't have asked to structure it this way in the first place. Unfortunately, like many terms in financing (see the rest of Sam's post), this is too often the case. Fortunately, it will have little impact on the company or your experience, so don't worry about it :)