Caesar's campaign in Gaul required some strong logistics as he dependend from using Gaulish roads to Narbonensis and Cisalpina from one hand, and supplies from his allies/client/defeated Gaulish peoples on the other. Almost every successful Gaulish attempt at defeating Caesar depended on their capacity to cut him from his supplies; and Caesar being a skilled general knew he needed to protect his armies both from attacks and starvation. Hence why armies were sent back in provinces for the winter or tasked with guarding roads and supplies in Gaul.

When Galba is sent to setup a camp in the Alps, it is clearly said that he was to protect the roads and Roman traders coming trough it (III, 1). The description of this camp is quite clear too : he took part of a vicus, possibly the chief place of the local pagus (an administrative/territorial division) as his headquartes, fortifying the place. It's not just a random camp but a way to take control of an administrative unit that had the capacity of percieving tools for its own chief people : Galba did the same in another Alpine people, and enforced the takeover trough taking hostages.

Caesar tells it as it is : Romans went there to ensure the way remained open under their control, not necessarily conquer this people as such. (III,2), and storing some reserves (impedimentum?)

When Galba manages to defend the camp but realizes the road can't be controlled, he simply ravages the region and leave in Narbonensis, close enough to intervene if needed.

Such a winter quarter, isn't just a tactical encampment, but had a strategical, political and logistic role to ensure supplies coming in Gaul, probably storing them too and keeping watch on strategical points.

When in Britain, Caesar sees no point at first to winter there, and stll accounts for his dependency on Gaulish wheat. (IV, 29)
Again it was something Gauls were aware of, and Vercingetorix general strategy was to starve Caesar out of supplies, attacking in the winter and spring, and then attack a Cesarian army deprived of supply going back to Narbonensis : Labienus victory in -52 and his capacity to protect Roman supplies at Agendicum (while Senones, who held this city, were revolted) where a wintering camp was built in -53 played a significant role into Caesar's victory at Alesia.