The nVidia 940m is too weak to make use of 4GB of video RAM since you are basically limited to playing games at 1366x768 / 1600x900 resolution using low or medium graphics. Plus DDR3 RAM is a serious bottleneck. 4GB of video RAM is only useful for games where the GPU is powerful enough to allow to play games at 1080p with at least very high graphics quality and uses DDR5 RAM. 4GB of DDR5 video RAM would likely be useful for the nVidia GTX 960m or faster GPU.
If you do photo editing, then 4GB of VRAM can be useful since it will...
The nVidia 940m is too weak to make use of 4GB of video RAM since you are basically limited to playing games at 1366x768 / 1600x900 resolution using low or medium graphics. Plus DDR3 RAM is a serious bottleneck. 4GB of video RAM is only useful for games where the GPU is powerful enough to allow to play games at 1080p with at least very high graphics quality and uses DDR5 RAM. 4GB of DDR5 video RAM would likely be useful for the nVidia GTX 960m or faster GPU.
If you do photo editing, then 4GB of VRAM can be useful since it will allow you to apply more filters.
Like I said, the 940m is too weak to take advantage of 4GB of VRAM. Games will not use more than 2GB unless you are playing with at least 1080p resolution and when using at least very high graphics settings. See link below for some benchmarks of the 940m.
In AC Unity the 940m gets about 28 FPS when running on low settings at 1024x768 resolution. That drops to 17 FPS when using medium settings and 1366x768. Using low settings and 1366x768 will be somewhere in between.
Below is a link that shows benchmarks for the 940m, GTX 950m and GTX 960m. Laptops with the GTX 950m generally starts at $800 and laptops with the GTX 960m generally starts at $900.