The level of distribution depends on the budget the film company/institution has. Conglomerates such as the Hollywood Big 6 (e.g. Disney) can afford a large tent-pole distribution of their film which involves lots of copies being distributed globally. For independent film companies distribution will probably be on a smaller scale to a more niche audience, often independent film companies focus their distribution to local areas, sometimes national, but they are less likely to distribute on a global scale. This is due to them having a smaller budget and unless they get funding from a larger institution then it is unlikely that they will be able to afford wide scale distribution.
In the past films used to be recorded on 16mm or 35mm film reels, these were often very expensive to buy and transport which is why unless a company has a big budget, they struggled to distribute that many copies. However now most films are recorded digitally which therefore allows companies to distribute more copies for cheaper, also it is more logistical as big reels don't have to be transported around everywhere. Digital distribution has made it far easier for independent companies to target a tent-pole audience due to it being far cheaper and therefore meaning that companies can distribute more copies with a smaller budget. This change has proved very convenient for many low budget indie companies.
In terms of the distribution of my trailer, I would target a niche, fairly local audience. I would distribute it virally and use other promotional forms (such as a poster) to promote it further. I would use the internet to distribute my trailer digitally because it is free and allows access to a large audience automatically. Almost all of my target audience of teenagers/young adults will use the internet, and probably youtube, in some way and therefore they'd be more likely to see my trailer and therefore be encouraged to watch my film if they enjoyed the trailer.
