They are meant to be informative. Maybe you have no idea on what XFP or SFP+ is because you've been running a Gigabit based network and haven't made the jump to 10GE yet - the debate might give you the top 3-5 points on why each might be the right option for you. And then, of course, there is a fun factor.
Tom
In most cases it isn't an option, you use what the hardware uses. I can't decide to use an SFP+ in a unit with XFP form factor. I select the hardware according to the features I need and then buy the optics it requires, I don't select the hardware based on the optics modules it uses. The only drawback I have seen so far is finding ER optics in SFP+ form factor but they might be available now (I couldn't find them a year or so ago). A good topic might be ipv6 migration strategies: dual stack or native v6 with nat64/dns64