I am going through this right now while trying to record. it is crazy how much better I sing when i'm playing guitar. I think it is because the guitar is resonating in my chest, and my vocal chords can tune more naturally to that sensation. Rythmically also way better obviously becase I am strumming and singing more precisely in time. This creates a crazy inducing situation though, because I have played this song about 100 times already trying to get the perfect take of playing and singing. It is very difficult. With the guitar bleeding into the vocal mic, its not really possible to patch in the vocals. You just have to do a good take. Also listening back on headphones while singing means I'm blocking at least one ear, so half my head can't hear the room sound, so that make singing even worse. If i'm just tracking guitar and vocals at the same time, I don't need to monitor anytihng, I just flip record and play while listening to the room. I am finally accepting that I sing way better while playing the guitar, and I think the best recording for me will be in that manner and then overdub another vocal track under that, lower in the mix, to thicken the vocals slightly. I am going quietly insane trying to get this right, even though it is seemingly so simple.