Argyle King
Legend
Assuming that you're talking about Glyph of Warding here:
(1) It's more reliable.
(2) It can give you more information ("Books! Fire!") which simply detecting a Glyph of Warding won't do.
(3) It's fast, a single action to cast. Glyph of Warding doesn't say how long it takes to detect glyphs using Investigation but there's no guarantee it will happen that quickly, and Investigation is generally considered to be a closer, slower investigation than Perception is. If you're checking a whole room for near-invisible glyphs it could take a while, and since "seeing/reading the glyph" is a common condition for triggering the glyph (according to the Glyph of Warding spell text), you may just get a Wall of Force + Cloudkill to the face. Find Traps may not do that, depending on how the glyph is worded. Ask your DM for details.
(4) It's not 100% clear, but the Find Traps description implies that "line of sight" need not include the actual sigil--it may detect the area affected by the sigil instead. Quote: "Thus, the spell would sense an area affected by the alarm spell, a Glyph of Warding, or a mechanical pit trap". If this is the case, then Find Traps would be the ONLY way aside from clairvoyance to detect Glyphs of Warding inscribed on e.g. the opposite side of an archway you're about to walk through.
Wouldn't the opposite side be outside of my line of sight?
Assuming no, I'm of the impression I'd still need to make the same skill rolls anyway if I wanted to disable it or avoid it. Though, I'm open-minded to the idea that I simply haven't witnessed the spell being used as effectively as others may have.