Firstly, for each organisation you are applying you need to understand their culture, values, type of business they do, their clients, how they compare to their competitors, where they fit in the market place, their brand, the 'language' they speak, the type of people they tend to hire (by looking employee profiles, Linkedin...), what previous employees have to say about them etc.
Secondly, you need to understand where the role you are applying for fits within the organisation and carefully decode the job advert / description / person specification.
Following that, you need to be honest and assess how well you fit the role and the company but also the sector. For example, you may want to work as a Marketing Officer but this role is going to be quite different if you are working for a bank as opposed for a Museum!
This type of research within you and the organisation takes time!
So, to answer your question, because it is so competitive to get a job in the current climate, it is important that you don't waste your time or the employer's. Do fewer but well informed applications, as it will be time well spent which will make you a more credible candidate, more likely to be shortlisted.
In addition, having a 'blanket approach' in your job applications is more likely to affect your confidence negatively as it will generate more rejections. If you do good applications, even if you don't get shortlisted, you will have learnt a lot about yourself and the industry in the process, knowledge that you can use in the next job application!