Many overclocking plugins currently available for the Vita simply unlock its maximum supported frequency of 444 MHz; they don't provide true overclocking. LOLIcon does push the CPU beyond its maximum limits, which comes with the standard overclocking risks: heat generation, system freezes and potentially shortening the life of your console's motherboard. On the plus side, though, it can help underperforming games operate more smoothly.
If you're interested in trying out the plugin for yourself, you can download it here. There are some bugs you may experience (lagging menus, for one), but the developer, dots-tb, had a team of testers try it out and it didn't brick or otherwise harm anyone's Vita.
It's worth noting that the name of the plugin, LOLIcon, is strange. It's a style of Japanese manga that portrays young and pre-adolescent girls with sexual characteristics. It's a pretty dark and disturbing name, to say the least.