Here is a spot that can provide for a lengthy discussion:
Manuel Ponce: Sonata III, first movement, mm. 47-50
Let us focus on the first beat of measure 48 (second bar of the example). The open E appears slurred to the following A. This suggests that both notes belong to the same phrase. I would instead consider the following interpretation: the E is the resolution to the line Db-D of the previous bar, and a new phrase begins with the A (second eighth of the bar). In support of this interpretation, notice that the downbeat chord (Fmaj7) does sound as resolution to the previous harmonic progression, the descending leap of fourth of the new phrase (A-E) derives directly from the theme, and this head of phrase is echoed–without a downbeat note–at measure 50. If we agree with this view, then we should not slur the downbeat E to the A, but actually play them slightly detached in order to suggest the end of a phrase and the beginning of another. One would think that the slur is more likely a technical one by Segovia than a musical one by Ponce. What do you think?
Regardless of our interpretation, the example illustrates how we should not blindly follow all the editorial markings on a score, but rather inquire why they are there.