What is the purpose of masking the LFSR value in STM32's noise generation?

I read on section 14.3.8 of the STM32F4 reference manual that you can mask the LFSR output value partially or totally.

At first I thought that it was used to change the pseudo random pattern (representative polynomial function) but I'm not really sure anymore.

What's the real purpose of this mask?

I'm not very familiar with LFSR noise generation so I might have got everything wrong...

According to section 14.5.1 of that same document the MAMPx[3:0] bits are used to control the amplitude of the generated noise (or triangle) waveform. For noise, they simply mask off (force to zero) the high-order bits of the LFSR output.