What are the tradeoffs for more coefficients for fractional delay filter?
More taps = more resources (multipliers and registers)
More taps = longer transient response, in some applications it can be a dealbreaker. It could cause significant pre-echo which can be problematic in some applications such as ultrasound time-of-flight diffraction.
More taps = better frequency response, your fractional delay will have a unity gain for a wider frequency range. Same for group delay.