I was wondering whether there's any problem in using the divider instead of step-down regulator.
A step-down regulator (Switching regulator) is better or required when the Power Dissipation using a voltage divider circuit or a Linear Voltage Regulator, is too high.
For example when you are powering a device from a much higher voltage source. With a 20V difference, even 100mA can generate enough power dissipation to consider using a step-down regulator.
In another example, using a voltage divider circuit or a Linear Voltage Regulator when you need to convert 5V to 3V for an application consuming more less 100mA is fine.
If the goal is to provide a 3V signal to an ic input, it's also fine since it consumes very little.
In the case of signal input, in order to limit current consumption, use high value resistors in your voltage divider: 22K or more. 100K is a common value. The total value between source to ground defines the power loss.
The main difference between a voltage divider circuit made off two resistors and a Linear Voltage Regulator (LDO or non-LDO) is that the Linear Voltage Regulator will always output the same voltage regardless of the input voltage whereas the resistor divider will only divide, not regulate the voltage. If the input voltage is higher, the output voltage will also be higher, proportionally, with a divider.
If your source voltage is constant and regulated, a divider is ok.
Linear Voltage Regulators also offer additional protections that you may want to consider. But high value resistors also protects the circuits effectively.