I used to produce and mix music for living some years ago. My perspective on using consumer speakers as studio monitors is as follows.
Consumer speakers vary in quality.
Studio monitors as a category are not standardized in any way. They also vary in quality and design dramatically.
The best studio monitors and the best consumer speakers are close in performance anyway.
Using average consumer speakers to nail the balance in a mix as good as using studio monitors is possible, but using average consumer speakers to dial in individual instruments during tracking as well as mixing is unnecessarily hard.
When you adjust a microphone's position and EQ to capture a live sound, you don't want a speaker with crappy frequency response and high distortion because you will compensate for it with mic placement and EQ to hear what you want. You want your individual tracks to sound great before you go into the mixing stage. That's where flat frequency response of the studio monitor is tremendously helpful.
If you work mostly with synthesizers and premade sampled instruments then it doesn't matter. They sound correct out of the box.
So then when you make a mix of those premade sounds, they will stack up similarly on flat FR speakers or less than flat FR speakers.
But if your vocal track is most prominent in a frequency range that other instruments are not using much, the speaker's frequency response in that range will affect your mix very much. For example if your speaker has prominent 1-2kHz bump and your instruments are not very prominent in that range, your vocal will sound balanced on the crappy speaker but it will sound weak on other speakers that are flat in that range. You will have nothing to balance the presence of the vocals against, just the natural bump of the speakers in that frequency range.
So you need to be super careful how you use the less than perfect speakers. They have their place in the studio, but some tasks are better done on proper neutral sounding monitors.
Consumer speakers vary in quality.
Studio monitors as a category are not standardized in any way. They also vary in quality and design dramatically.
The best studio monitors and the best consumer speakers are close in performance anyway.
Using average consumer speakers to nail the balance in a mix as good as using studio monitors is possible, but using average consumer speakers to dial in individual instruments during tracking as well as mixing is unnecessarily hard.
When you adjust a microphone's position and EQ to capture a live sound, you don't want a speaker with crappy frequency response and high distortion because you will compensate for it with mic placement and EQ to hear what you want. You want your individual tracks to sound great before you go into the mixing stage. That's where flat frequency response of the studio monitor is tremendously helpful.
If you work mostly with synthesizers and premade sampled instruments then it doesn't matter. They sound correct out of the box.
So then when you make a mix of those premade sounds, they will stack up similarly on flat FR speakers or less than flat FR speakers.
But if your vocal track is most prominent in a frequency range that other instruments are not using much, the speaker's frequency response in that range will affect your mix very much. For example if your speaker has prominent 1-2kHz bump and your instruments are not very prominent in that range, your vocal will sound balanced on the crappy speaker but it will sound weak on other speakers that are flat in that range. You will have nothing to balance the presence of the vocals against, just the natural bump of the speakers in that frequency range.
So you need to be super careful how you use the less than perfect speakers. They have their place in the studio, but some tasks are better done on proper neutral sounding monitors.