I take you mean versus using a second carboy and only racking once each time. There are wine makers that take your approach (usually due to space or cost issues) and it, by and large, works fine. I do see 3 modest potential issues. First, there's the time involved. For me, cleaning and sanitizing is not much fun. Second, racking brings the risk of introducing air into the wine, particularly at the beginning and end or when the siphon tip is exposed. Third, wine and yeast prefer to be left alone as much as possible and don't like to be stressed.
By the way, I assume you re-clean and sanitize the siphon equipment, as well.
Tony P.