You mean a chord made from these tones: 1–3–5–7b?
Or in the case of a 5 chord, tones: 5–7–2–4.
I like using them on particular songs, like blues. Mostly, I find the major chords work just fine for me. It all depends on one's taste.
V7's sound just a bit 'unresolved' so are great for adding a bit of drama to a song. Great for blues songs, like Carl says, and also for songs like 'Five Foot Two, Eyes of Blue', that have that wonderful walk up of 7ths in them, A7, D7, G7, C7 etc.
Whats a “V7” ive never heard of that in my 6 years of playing, and I know a lot of chords probably all the 7th chords.
V7 just means the chord a fifth away from the root chord but includes the extra note to make the 7th. I believe the system is called I, IV, V or Nashville Numbers. I is the root chord, say G, IV ( the chord a fourth away from the root) would be C and the V (the chord a fifth away from the root) would be D. D7 if you wanted to play the V7 chord. Hope this makes sense and answers your question. Jan