Not the GP, but for the products I look for Galaxus has occasionally been among the cheapest.

because I care more about service than about 5 CHF.

Their website - and tech in general - are way better than the competition. Their prices are competitive (sometimes the best, sometimes not, but rarely an unreasonable rip-off). I often prefer local pickup over mail. They already have my information on file, I don't need to futz around with making an account.

Price comparison sites are fine if I know exactly the item I want, less so if I just have an idea of the category.

It's not that I buy everything there. But it is my default option.

Because consumer protection is nonexistent and it's easier to just go with Digitec/Galaxus where you already have an account than figuring out if this dealer is trustworthy, shipping in a reasonable timeframe, and whether they will be a PITA to sign up with.

The filtering system was way, way better than everything else we had for a very long time and they often also where the cheapest. I write was because honestly I haven't visited many other shops for quite some time. But whenever I check on toppreise it's only marginaly more expensive then the other shops. It's convenient to have everything from the same shop where you know you have it the next day. And the "Geiz ist geil" mentality just doesn't realy exist in Switzerland.

Reliability, consistency, convenience, laziness. I know by and large if something goes wrong, Galaxus will just refund me no questions asked. Having tried some other retailers (that I found on toppreise)... that was not always the case