Before the days of the internet and social media boom, many jobs were filled by people that had dropped their CV in to a company. Sometimes they may have been stored on file for a number of months before a position came up that the candidate was suitable for.
This was often a long drawn out process, and unless you were lucky enough to drop on a company when they were looking for someone, it was very much of a waiting game.
If you are currently looking for work though you should not rule this out. Many employers still like it when someone takes the time to come round and personally introduce themselves and leave a CV. It also give the candidate the opportunity to talk to the company about why they want to work for them and the skills that they have that they feel may benefit the business. If you are serious about job hunting then it cannot do any harm, so register for all the jobs boards online and upload your CV but why not also pop in to a few companies that you are interested in and leave them your details.