Personally I don't think there is a need to keep to one set temperature, unless you want to experiment, and as a hobby rather than just making cheap beer, most want to experiment.
Unless you hold the temperature steady, when you try something new, you simply don't know if it was temperature or what you have done to the brew, early days I wanted best value for money and a high ABV, so I noted the sugar added varied from 1 kg to 1.5 kg kit to kit, so tried to increase sugar, I took it up to 2.5 kg which had so many off tastes it was nearly undrinkable, or was it? By time I had got to 2.5 kg I had also hit summer months, today more worried about taste, so want to reduce rather than increase sugar, also looking for a low ABV that means I can drink for longer without falling over, my whole idea has changed, since it costs so little really not worried about ABV. However those early days I made so many mistakes because I thought it was what I had changed which made it better or worse, where often it was simply the temperature.
So yes to produce cheap beer the temperature is not that important, but to experiment then it is, including of course experimenting with temperature. Personally I aim to keep brew as cool as it can be kept in early days, once first week over, does not really matter, my one experiment with Lager taught me one lesson, you need to yeast to produce alcohol early in the process when using unboiled tap water, it is easy in the first few days to get an infection, all well and good when all water is boiled, but with a beer kit, it is tap water, so you need a reasonable quick start to stop infection, and a cool start to reduce off tastes, temperature control allows you to brew in the happy area where quick enough to stop infection but slow enough to stop off tastes.
Of course I call them off tastes, some people may like that taste?
