My grain of sand, according to my own mobile struggle is;
1) no to HUGE objects. (even empty space in a sprite needs to be calculated for rendering, so it eats up processing power anyway)
2) NO to too many collision checks
3) no to too many objects doing too many things at the same time
4) no to unnecessary workaround processing. You need to think up that efficient formula every time.
5) Separate things into different layouts if you can.
the 4th point is really important to me. I'll give you an example from my own experience:
I made a game a while back, and needed to show the final score after the game ended. and i wanted to be cute and re-count it in real time. For this i had made a formula so it didn't take too long to count when the score was too high. so i told the game to add a sqrt(totalscore)*3 to the final score counter. It did work, but the game had to calculate this for every time it added the fraction to the score.
Eventually, since it wasn't very efficient, I added a variable to store that fraction given by sqrt(totalscore)*3. i just calculated it once, and then i added the variable, instead of the formula, to the finalscorecount thing. and the fps went from 5, to 60 in a heart beat. and i was so happy.