I am buying some new sheet music online but the the music I am buying includes Piano/Vocal/Guitar. I assumed that you could play all three individually (without the others) but when I look at the notes, the piano (which is what I play) only has afew notes in each line. So my question is: With Piano/Vocal/Guitar sheet music, Does the piano have to have a guitar (and voice) playing at the same time for the song to sound good? (In other words: If I only played the piano for PVG would the song still sound normal?)
A few caveats to buying sheet music:
Music for "piano/guitar/voice" often does not have the complete guitar version. If you are a guitarist, look for TABs to lend a possible greater authenticity.
If the music is labeled EASY or something similar, then it is unlikely to be anywhere near authentic.
Some sheet music will leave out the melody, some will not. (Three sides of the same coin:)
Real music often lets the singer carry the melody. This means the melody may be missing from the piano part and if you are not singing to it, you may miss the melody. This is hit or miss.
Some sheet music has the melody where the real performance may exclude it. This is hit or miss. If the melody is included in the music, it is possible the whole arrangement is substantially different then the actual recording artist's arrangement.
Often the piano part in sheet music is designed to sound good on it's own, at the expense of authenticity. Of course this is hit or miss.
Sheet music is never written by the artist, and while there are good and bad things about this, one of the most relevant is that while transcriptionists can be very good, it is possible for the transcriptionist to get a major concept as to how the piece works on the instrument wrong. And it is impossible to eliminate all mistakes.
Artists can and do change the way they play a piece from time to time, causing some arrangements not to match what you want to sound like.
As @AJFaraday correctly notes, you must use your experience and your ear to guide the way you want to interpret sheet music. Often the music is a guide rather than a definitive prescription of how to play the piece.
This depends on the arrangement. Often you will see music which has scores for piano and one singer, with chords over the score. In which case you can expect the piano part to sound fine on its own.
If there are notes in place for all parts, you can probably expect there to have been more thought put in to how the parts play together and interact. Removing parts might be more difficult.
The easiest way to find an answer to this kind of question, however, is simply to start playing. See if it sounds right to you.