Why using a IR sensor instead of a IR sensor module (1838B)?
The black LED is photo transistor. This means the current through this part is controlled by the IR light intensity on a certain wavelength. The output is a real analog signal without any processing and signal forming.

The three pin 1838B is an IC, which is also a IR receiver with integrated pre processing of the analog signal. In this particular case this devices has a \$38\,kHz\$ filter, which corresponds to the IR carrier frequency of some IR remotes. It also demodulates the IR signal and generates a digital output. Perfect for reading data from remotes.

According to your use case, you can pick either of them.