As jaykay says. The thing about using the full course is this. A bacterium which has been exposed to but not killed by an antibiotic has a good chance of now having some genes that code for resistance to that antibiotic. Not only does that make this bacterium and all its offspring resistant to that antibiotic (and probably a number of related ones, too) but also, bacteria can pass these genes between each other - and between types of bacteria, too. So the resistance spreads like wildfire and across species. By using the full course you are doing the best that you can to make sure that all exposed bacteria are well and truly nullified and don't survive to build resistance and pass it to other bacteria.
It's something to think about befpre choosing an antibiotic that requires more than one shot. If the shot makes enough of a difference, can you still catch the patient and administer any subsequent shots? If not, use a Long Acting or one-shot antibiotic.