Vin Pin as 5V output in NodeMCU ESP8266 12E

Yes you can use it but also note that, the Vin pin is directly connected to the Micro USBs Supply voltage so in simple words whatever your USB will give the power same power will be outputted to Vin pin. So here your micro USB pin is outputting 4.9V so the same voltage you can read with digital multimeter.

Also note that you may not control the voltage i.e. it will fluctuate between voltages so suppose( 4.6V to 4.9 or other range. Also I would recommend not to connect 500mA current to Vin pin as it can affect your computer also can cause shut down. There is no back-power protection on the board.

So be careful. Also if you Vin pin is used to power the ESP board if you wil use it for output then you  won’t be able to power through it. So you will only have one source to power it i.e. micro USB port.  

The answer to your query is both yes and no. Yes for that because you say that you connect your NodeMCU with your Laptop/PC through USB cable, where the voltage of the USB port out is 5.0V, which you measured, shown 4.9V, you can use this power as input for nodemcu and as well as the other sensors attached with it. But on the other side, no because the USB port has very low current rating i.e., max by 500mA. If you connect NodeMCU and some kind of sensor to power up both of these, there might be maximum chance of your PC USB port get damaged. I prefer to use a separate 5V and 1A power supply or power bank battery for your hobby projects. Here I would like to suggest you to contact with SSLA technical support team for better assistance in your projects.

The answer to this query is both yes and no. Yes, for that reason because you say that you connect your NodeMCU with your Laptop/PC through USB cable, where the voltage of the USB port out is 5.0V, which you measured, shown 4.9V, you can use this power as input for nodemcu and as well as the other sensors attached with it. But on the other side, No, because the USB port has very low current rating i.e., max by 500mA. If you connect NodeMCU and some kind of sensor to power up both of these, there might be a maximum chance of your PC USB port getting damaged. I prefer to use a separate 5V and 1A power supply or power bank battery for your hobby projects. Here I would like to suggest you an advanced product EFB-IoT by Sierra Software Ltd. with multiple specifications along with technical support from their team for better assistance in your projects.