This is such a debated question!
In simple thinking – YES it is always best to answer every question. However there is one thing for consideration here, and that is the evaluation. If the tender document states that all questions must be answered otherwise your submission is null and void, then you must answer all questions.
Often in public sector tenders not all of the questions are scored or evaluated, so on these occasions you may be able to not answer questions, but in reality if you don’t answer all of the questions the buyer is imply going to think “why haven’t they answered these questions, have they got something to hide?” which when scoring is being considered won’t support your submission at all.
The best practice method would be to answer all of the questions which are posed.