This is a very important question and thank you for bringing this out. Of course you already know the work of solar panels. Now you asked if solar panels can be used in smaller systems like 10W panel.
In simple answer, smaller solar panels usually do not need a charge controller but it will ultimately depend on the configuration and technical specifications of the gadget you want to power with solar, for example the voltage and current range it can safely accept.
But you can still determine this by doing some quick calculation. Divide your battery Amp hour capacity by the maximum power amp rating of your solar panel no matter how small. You don’t need a controller when your answer is above 200.

Understood, thanks sir