A thoughtful question. Should we really be spending our time on things that we need not know? Is it worth being educated on things which we can do without? For instance, does one need to be educated about picking up what he/she requires at a shop? After all, isn't that something everyone can do, because it is something purely based on one's own decision?
The most important factor to consider would be the importance of education concerned with a particular person. If a student wants to become a lawyer, it is important to educate him/her about law rather than making the student derive a complex equation or formulae! Relevancy is the key.
Thinking practically, while doing a last-minute revision for an exam, what are the things we would concentrate and spend our time on? It would undoubtedly be on those topics which we know are important and are sure of seeing in the question paper. So, we are clearly deciding that we are concerned about what will be useful rather than doing things randomly.
The same implies to education. Those interested must be educated with the subjects they like. Why should a student who is going to become a surgeon require to know how to do complex calculus? Even the graduates after engineering don't always use them! The same way an engineer or a lawyer may not be interested to know all the scientific names of animals which they will never be dealing with.
Education must be given to all; a politician must be educated about how to be a good leader, an artist must be educated about colours and patterns, a singer should be educated about chords and tones, a writer must be educated about words and vocabulary. That would be relevant education which would make the student better at whatever they are interested in.
There will be people who would argue that knowing everything is important. Why should an engineering student need to learn all of important fields of engineering for two whole semesters, when the student has already chosen a branch of interest? The answer you would get is, to know all fields of study and to respect them.
If we are to value each other's role or job in the society, then we must know what they actually do. But this does not mean that we have to learn all the things they have learnt! We must be educated enough to know that every option and job in life has its own importance. This would save all the time we would have to spend on things we never wanted to, but instead use that time to make ourselves better at what we like doing and what is useful to us. To conclude, our education must focus on what is most useful to us. This is what is needed in the long run. Additionally, we must be moderately educated on things that might be useful in someway. In the end, its all about prioritising the "usefulness" of things.