I'm no expert by any means and as you bring up an interesting question here's my two cents.
A charge controler is just that, it controls charging and is not a load controler although maybe there are some units that do both.
So as your question is about charge controlling or charging in general I'll talk about that.
First of all efficiency is a tough one to get a hand on as I'm not sure what that usually means.
In a perfect world a direct connection to the batteries would be the most efficient as any time you add another component into a system it likes to get paid so what goes out is less then what goes in (no free lunches ever).
Reality on the other hand is quite different.
You just can't throw all the charging current into a battery and expect it to charge up. Oh it will but if the current is to high you'll ruin the battery in short order ( this may happen in a direct connected system).
In terms of charging I lean towards (and have the best results) with a PWM three step charging process.
In the first step (Bulk) the charger will put in the max amps the battery will take to bring it up to a bulk voltage setting.
In the second stage (Absorption) current will be varied (usually decreasing as the battery carges) to maintain the bulk voltage.
In the final stage (Float) current is reduced and varies to keep the batteries at the float setting.
Excess power is diverted elsewhere and if not used it is wasted.
Do a Google search on batteries and you'll find a wealth of info on charging.
Of course a lot depends on your battery capacity and charging system, be it solar, wind, hydro or el-cheapo battery charger.
If your charging system is less then C5 (5% of amp-hour battery capacity) then you probably don't need a charge controller. Above that you run the risk of ruining your batteries without a charge controler (human intervention is a form of charge controller).
Boy that was a mouth full, hope it helps.