it's largely pointless having more than n tiles developed round a size n city (as by definition no-one will be there to work the tiles).
This isn't always true.
For example, in my present game my capital has got:
(a) three high-food (4 food) commerce tiles (clams, coast, financial trait)
(b) four low-food (0-1) production tiles (mines)
(c) a load of food-neutral (2) commerce tiles (grassland cottages).
But, thanks to the health/happy cap, I can't grow the city large enough to use them all at once.
So, to get the most out of my economy with the tiles and population available, it makes sense to work (a) all the time, and to switch between (b) and (c) as necessary.
This approach uses the (c) tiles to grow the cottages and population whilst researching to a specific tech (Writing for libraries; Iron Working for swordsmen;etc.), then uses the (b) tiles (and the whip) to build the newly available building/units, before switching back to the (c) tiles to chase the next tech target (and to grow back the whipped population).
Improving those extra tiles (the city currently has 12 improved tiles and varies between 7 and 9 in population) is vital for this kind of early-game micromanagement.
It isn't always the best policy, but in some situations it can be the difference between getting up amongst the tech leaders and getting left behind.
Also, personally I just don't trust the worker automation or the city governor to make the right choices (a civ3 hangover?) and so always do my management by hand. It can be a little tedious when your civ gets larger, but, having seen the improvement patterns of the AI civs, I reckon it gives the human player a definite edge on them (if he/she makes the right choices, of course).