I do both. In my case textbooks are to fill theoretical needs/gaps. I go through full books in some cases and in others it is not feasible based on various factors (difficulty of subject, need, content, 500+ pages etc.) I find that some of the newer textbooks give a helpful flowchart of chapters so one can choose their "adventure" based on interest or the curriculum needs (of an instructor).
On occasions I abandon reading after a chapter or two if I don't think it serves my needs or the subject matter is too difficult for me. In the latter case I may try to look for an alternative or come back to it once I have gained pre-requisite knowledge.
On occasions I abandon reading after a chapter or two if I don't think it serves my needs or the subject matter is too difficult for me. In the latter case I may try to look for an alternative or come back to it once I have gained pre-requisite knowledge.