Could you get more done by leaving work early?

I usually relax after I did something relevant in the day, doesn't matter if it's in the first hours of work. At this point, the feeling of "mission complete" makes me loose focus and use the following hours to do non work related stuff.

On the other hand, I feel bad when I did many small things during the whole day but could not complete many of them. After the day is finished, it's hard to point what I did and the day does not seem to worth when this happens.