If it happens once, it's not going to affect much. But if it happens fairly often, that's an indicator of damaged posts in lead-acid batteries or other issues. Constantly draining and charging a battery can cause it to "bloat," which could lead to dangerous cracking and leaking (battery acid is extremely caustic and toxic), or even explosions and fires. Moreover, corroded posts are an indicator of damage, so be on the look out for white or greenish flaky buildup where the wires connect to the battery. If it's very light buildup, you can disconnect the battery from your car and clean the posts and connections with a wire brush. But if the build-up is excessive, it's time to change out the battery. Thankfully, many automotive retailers give you discounts on new batteries if you bring the old one in to be recycled.