I meditate to awaken (in the deeper sense), to bring calm to a wild mind (as I think Robert Pirsig said, peace of mind is not the most important thing, it's the only thing), and to try to become a better, more compassionate person. You don't have to meditate in a convoluted sitting position if you choose not to (although there are good reasons for sitting in lotus). I would start by just regularly sitting or walking…
I have been meditating for a while, always sitting in a chair. What are the advantages of the Lotus?
Someone has already quoted Wikipedia, so I won't repeat it, but most of those sound like benefits that you can get by lying down, or finding a really comfortable chair, or something similar. And the bit about improving digestion sounds especially dubious, since it doesn't really say what that means, and a lot of Yoga folks have a bad habit of making vaguely shiny-sounding medical claims without evidence.
(Do I sound negative? I actually do sometimes meditate, because it's a pleasant thing to do. I just want to make sure I'm not fooling myself about why I'm doing it.)