Why do most people use fillets over fiberglass tape for joining panels? Having done both I prefer the look of fillets but I would rather work with tape on the joints. Is there some advantage of fillets over tape?

My niece has abandon her boat project and I have given up on her. I am very disappointed too but that's another story. I am thinking I am going to finish it myself to use or loan out. Or I might put it up for sale once it is done. My wife said name it 'WasGonnaB' (As in was gonna by my Nieces boat) and just finish it. My niece is obviously not going to!