Yes, it is kind of necessary for this current generation of games and future games as they use more Video Ram (VRAM). Max Payne 3 is known to use a lot VRAM and some other heavy graphical games such as Metro. This is if you play at 1920x1080p or higher, playing at high graphics settings, and/or if you plan to use multi-monitors.
Now, the funny thing about the GT 640M LE is that there is too many variations on it and we can't tell if it's either the GDDR3 or GDDR5 version.
The only way to know is by using a program to see the actual hardware specs such as GPU-Z.
Anandtech's NVIDIA's GeForce 600M Series: Mobile Kepler and Fermi Die Shrinks
We've also seen the Acer M3 with the GT 640M, which did have 384 cores clocked at 625MHz. (It also used DDR3 and was paired with a ULV CPU so it doesn't represent the maximum performance we're likely to see from the GT 640M.) Note that all of the announced 28nm Kepler parts currently use the GK107 core, but NVIDIA has not provided details on the exact core counts yet. In fact, let's just get right into the crux of the problem.
Yes, NVIDIA is up to their old tricks again with the GeForce GT 640M LE (and given some of the above, we might see even more variations on the other parts as well). I thought we were over this after the marketing nightmare that is the GeForce GT 555M. That said, if history has taught us anything, it's that any chip that supports both DDR3 and GDDR5 is almost always going to be running DDR3 once you get into this performance bracket. I'm honestly not sure how we're going to be able to tell the two GT 640M LE's apart in the marketplace, though, outside of waiting for reviews to surface, and that bothers me. Our best advice is to make sure you research what you're getting if you want faster GPU performance.
Unfortunately, just like the two GT 640M LEs, there's just no way to tell which version you're going to be getting. Ultimately, we expect the 40nm parts to all disappear and be replaced by 28nm variants, but we'll have to wait and see how that plays out.
Update: NVIDIA has now posted their spec pages for the above GPUs. I've gone ahead and linked them in the above table and updated a few items. Worth noting is that the GT 650M now lists clocks of 850MHz with DDR3 and 735MHz with GDDR5. It looks like both versions will have 384 cores, so OEMs will choose between more computational power and less bandwidth (DDR3) or less computational power and more bandwidth (GDDR5). NVIDIA suggested that their goal is to keep products with the same name within ~10% performance range, and the tradeoffs listed should accomplish that goal. I'm also inclined to think GK107 consists of two 192 core blocks now, as every product page using that core only states 384 cores, with the exception of the GT 640M LE, but we know 640M LE will have both 40nm and 28nm variants. In general, we'd suggest going with the 28nm GDDR5 configurations when possible, as 128-bit DDR3 has been a bit of a bottleneck for even 96 core GF108, never mind the improved Kepler chips.