You get a handful of somewhat questionable benefits. If for some reason your guests are visiting your printer's administration page, they won't have to click through a scary warning page. If someone is somehow sniffing all the traffic within your home network they won't be able to get your printer's administrative password.
But the main reason is some homelab enthusiasts are like bodybuilders at the gym - taking on tasks that seem Sisyphean to outsiders, for fun and to build their strength.