General speaking, we need 1 channel per GPS satellite. There are only 30 satellites in the system & why we need so many channels in the GPS receiver/logger?
According to GPS algorithm, bigger number of satellites a GPS tracks at a time, better accuracy the GPS can calculate.
In a period of time, some GPS satellites disappear from horizon & GPS receiver lost connection from them. Meanwhile, some other GPS satellites appear. If the GPS is not able to “capture” those newly available satellites fast enough, the number of satellites track by the GPS is reduced. Hence the accuracy will be reduced.
The speed of “capture” those newly available satellites are very important. In order to speed this up, GPS receiver must reserve a big number of channels for searching new satellites all the time. You know, searching new GPS satellites is time consuming. That is the reason so many GPS channels is needed.
Same theory apply to GNSS.
GNSS receivers usually have more than one Navigation Satellite Systems. (e.g. GPS, GLONASS, Galileo, BeiDou ...). More channels, faster position fix and better accuracy for them.