Fresh water tank maint. breaks into a few basic discrete areas.
Changing water
Vacuuming
Filter Media Cleaning
The rest (algae scraping, plant pruning and fertilization, etc.)
Each is needed for different reasons and can be performed in a number of different ways. I could write a few pages on each area and likely not cover it all I think. But some quick thoughts.
The bacteria is everywhere in a tank. There is more outside of the filter than many realize. The less properly and often one maintains the filter media, the more bacteria will be somewhere else. Allowing bio-media to clog is the main culprit.
The bacteria which is living in the substrate is not on all the substrate. It is in the top layer of the substrate, where food and oxygen are readily circulating (an exception is in UGF/RUGFs where the entire substrate is the bio-media). Moreover, the bacteria is photosensitive, so it is on the undersides of the pieces of gravel or grains of sand. Vacuuming can disturb it to some extent. Doing a deep vacuum which turns over the top layer and what is below for sure will effect the substrate based bacteria. It is one thing to vac off surface junk regularly vs doing deep vacs all the time. The latter are usually best done in sections over a few weeks.
Changing water is pretty much a good thing. There are a few instances where it should be put on hold- for ex: fish are in the process of spawning- don't interupt it. You ran out of the required dechlor, go get and then do the water change. I am still waiting for a post claiming fish died from the water being too clean (note this is not the same as being too pure). But the key to changing water only about what comes out, its as much or more about what goes back in. In many cases the new water is restoring things that have been used up by the tank and inhabitants. So doing weekly changes for a tank with average stocking is a decent changing guideline, imo. As tcamos noted, some tanks can go a bit longer and others not that long. Many higher tech planted tanks need the nutrients reset every few days.
Filter maint. means not only insuring good flow, it means getting out the trapped solid wastes, especially the organic ones. Even if they don't completely glog up the filter flow, the will eventually degrade into small enough particles to exit the fine media and go back into the water column.
I have kept 16-18 tanks for over 10 years now. For the most part I have changed the water and cleaned the filter media almost every single week. I have vacuumed some tanks (bare bottom ones) every week and some with plants a few times a year and with heavy planting almost never. This year has been an exception due to non-fish issues until very recently. Even so I would say my record on weekly maint. is over 90% for sure. That is a lot of time and effort- trust me when I say I would not have spent that time if I did not think is was beneficial. Oh yes- big tanks are more forgiving of missed maint. than small ones, lightly stocked ones overly heavily stocked ones as well
Oops, I got long winded again. Sorry, but I hope it helped some.