There are two aspects to this:
1. What job you are looking for
If you don't care about the company at all, but only about the position, your strategy to primarily go by the job description is valid - as long as the job descriptions are providing all the information you need to decide whether you are interested in the position. A job description typically has two types of information,
1) what you are required to know and 2) what you will be doing at the job.
Sometimes there is also a bit additional information that gives you a hint at how you will be doing that at this company, i.e. a flimsy glimps of work culture.
However, for many people other aspects are relevant as well, e.g.
- what industry is the company operating in: many people do not want to work for the military or for an NGO assuming pay will be bad
- what size is the company
- what hierarchy (flat/deep) has the company
- what age structure has the company
- what products does the company sell
If such general aspects are of no concern to you, i.e. you're primarily concerned what you need to do and what you need to know to get hired, then your approach is fine to decide which job to apply to.
2. What recruiters look for
Another aspect is what recruiters look for in candidates. Many recruiters want to make sure a new hire will stay long-term with the company and really wants to work there. One method they have to gauge how much you want that particular job is in checking how much effort you put into preparing that one application/interview. To do so, they might ask how well you know the company and maybe try to verify any claim by asking specific questions. The more you know, the more time you obviously spent researching the company. It's also always a plus if you can present yourself as interested in the general area the company works in, as this might indicate more enthusiasm to learn the particular knowledge domain.
So, if you do not spend time to get to know the company beforehand, you might lower your chances if a recruiter follows this approach.
Note that it's a trade off. In particular, if you really don't care which company you end up with, you can either apply to more companies or prepare yourself better for less interviews and the overall chance to score a job might be about the same with the same time-investment (just invested differently). It's up to you. If you however really want a particular job, it's definitely helpful to know something about the company.
As to what is expected, the more you know the better, but typically it's already enough if it gets clear you know what company you are currently interviewing for and what it roughly does. Let's say you apply with Tesla, you should know they make cars and are pioneering electric cars in particular (and that hopefully is totally fascinating for you).