Modern bikes don't really need maintenance. IMO this has led to a modern mindset that you only need to work on a bike when something is broken. Vintage bikes, because they didn't have sealed bearings, needed regular maintenance. I've noticed maintenance and restoration or repair tend to get conflated nowadays. They have different requirements. This leads to needless disagreements about such things as whether fixed cups should be removed, or freewheels greased.

Let's maybe not get too into that now, but it seems that we could use a thread for what correct maintenance was for C&V bicycles. So from memory here are some of the old general guidelines. This is all stuff that was drilled into my mind BITD. Clearly some folks were more fastidious about maintenance than others, but if you wanted your expensive fancy 10 speed to last, it was wise to follow the old rules.

There were several rules of thumb. First, all bearings were overhauled about once a year, plus again after any time you were caught in serious rain, plus whenever they got dirty. That's why we used white lithium grease, Campagnolo or generic. When it starts to go gray, you know dirt has gotten in the bearings and it's time to repack. Another ritual was carefully listening to bearings spin. If you heard the subtle telltale sound of a tiny piece of grit, it was time to repack. On average this might have added up to two or three times a year. Usually the hubs and BB needed more repacking than the pedals or headset, but all of these were done once a year. At least that was what you were supposed to do.

Chains and freewheels got a monthly cleaning bath. Chains were replaced when they started to 'stretch' -- same as now, and freewheels were replaced when the chain started to skip off the teeth. This was on average after about two chains. Freewheel life also could be and often was prolonged by replacing individual cogs.

Cables got pulled and greased maybe once a year, and were replaced if necessary. No linings in housing then. Brake pads didn't need replacement as often as now, because they were thicker than modern pads, a result of side pull brakes having less alignment error as the pads wear in.

Wheels had to be trued regularly to stay straight. They would get rebuilt with new rims and spokes when the spokes started to break or notch at the crossings, or the rim cracked, or tension had gotten excessively uneven from continued truing. Spokes weren't generally reused unless the wheel died an early death.

Obviously I'm talking about racers and enthusiastic club/century riders who had expensive bikes. I'm also assuming the bike is ridden nearly every day. BITD most people had just one good bike, because they were expensive, and therefore they got a lot more miles than is common nowadays.

Your average joe who bought a mid level bike shop bike and left it in the garage most of the time rarely did anything.