Video Bandwidth (VBW) is basically a smoothing filter to reduce the variation in the noise as much as possible and allows measurement of low level signals.
In analog (swept) spectrum analyzer, VBW is implemented by introducing a low pass filter (LPF) after the detector (i.e. after resolution bandwidth (RBW) filter).
In software defined radio approach, as used in the RTSA, the VBW filter is physically absent. Hence, a solution to implement VBW is to emulate its behavior of swept spectrum analyzer via averaging the spectra of the acquired data. The number of averages depend on the filter type. However, the differences among different types of filters are so small. Accordingly, changing the filter type can be negligible, especially at low RBW:VBW ratio.