Upsampling by 4 in DSPs

Hello,

During my readings in DSP for SDR implementations, I found the upsampling
ratio of 4 in 2 different locations through modem designs. One at
digitizing the IF signal and one at upsampling before pulse shaping. My
question is about the reasons of choosing the ratio of 4 for these two
cases. I am elaborating on them in the text below:

1- For IF sampling at the receiver. Some designs choose to oversample the
IF signal by 4 which means the fs=4IF. Is the main reeason behind this
ratio is to allow for efficient downconverting stage since the DDS will be
replaced by simple Mux? But why other designs complain about this fs=4IF by
saying it is subject to alliasing by mixing harmonics? So should we use
this ratio here or not? or it is about how good our mixer before ADC?!!!

2- At pulse shaping at the transmission stage, many designs choose to
upsample by 4 (and some choose even 2 but I feel the majority goes for 4).
Is the reason behind the ratio of 4 is to allow phase and frequency
tracking since if we upsample by 2 then we can only track the phase but not
the frequency shifts of the signal at the receiver? Is this true?

.