Although, as I've just written, I cannot think of any reason why anyone would deliberately fuse (only) the neutral, historically speaking, double-pole fusing (L and N) seemed common. I may be wrong, but I have the feeling that this was once even true of at least some cutout fuses.
Back in the 60's, and perhaps a little beyond, I built umpteen mains-powered PSUs. In those days, it seemed totally 'standard' (probably for no reason other than "that's what we've always done"), at least amongst amateurs, to put fuses in both L and N of the incoming supply (as well, often, as some fuses on the outputs) - and we routinely used Bulgin panel-mounting dual fuse holders, which seemed to exist primarily for that use, for that purpose (the left hand one in the below dusty/rusty photo - the RH one is for outputs {and the actual fuse carriers are currently 'somewhere else!}) ....
However, I guess that we had thought about the potential problem of doing this since (as can be seen in the photo), we usually put panel-mounted neons between L and N on
both sides of the fuses (the two green neons) - so that one could see that the equipment was still 'live' if only one of the fuses (particularly the L one) had blown.
However, why we did it, other than because of 'habit', I have no idea.
Kind Regards, John