Which approach to studying is better?
It is good if you can understand something completely and thoroughly. However, there comes a point where most of us must leave gaps and accept that the gaps will fill with extended experience and exposure, over time (technical term: "by osmosis"). Failure to accept that gaps need sometimes to be tolerated can lead to collapse of careers. 

What you need to judge is how fast you are moving - if you do not trail back too much with respect to what's required in your duties, I would not worry too much. Good understanding is a worthy cause and will pay dividends later on. However, when you fall back or fail to address important aspects of your studies (or repeatedly fail, through perfectionism, to submit reports/works/papers on time), then you should consider ways to get a coarser, higher-level view of what you need to learn and start to leave gaps.

Hopefully these criteria will help you to judge at which level you may want to operate and to switch between levels when required.