I've rendered up to six projects at once. I took copious notes on render times.

What I found was that the overall time to finish the renders was about the same, but I had the advantage of not having to babysit my computer in order to start the next render, during times when I was away from the computer. So in essence it was a time saver.

Batch renders or multiple instances of renders are very possible - they do not "save" time - they can just execute a semi-automation style of activity.

Batch renders or multiple instances of renders are very possible - they do not "save" time - they can just execute a semi-automation style of activity.That is not always true. First of all, if all your CPU cores are not utilized with one render, then a second render can proceed at almost the same speed as it would if it were the only render being done. In this situation, you can cut in half the time needed to complete the renders.

Second, if you use multiple disks, you can avoid any disk thrashing that might actually increase the overall time for rendering.

I do multiple renders (using multiple instances of Vegas) every single day and have done so for a decade. It saves me a huge amount of time compared to doing the renders one after another.

I also use various batch render scripts, some of which I wrote. They save time in a different way because you don't have to "baby sit" your computer waiting for one render to end and the next one begin. Any time between renders, where you fail to realize that the render has ended, is time lost. With a batch render script, there is zero time between renders.

Also, batch rendering lets you do multiple renders during times when you can't attend the computer, such as overnight. This saves a huge amount of time because you can do a dozen half hour renders overnight.

I can go on, but both batch renders and multiple instances of Vegas, each doing a different render, will get your work done much more quickly.

by multiple disks I assume you mean multiple source and multiple destination disks?

so a 2 disk project would take 4 disks?

Multiple disks are not an absolute requirement, but if your render doesn't require a lot of CPU time, then the render can actually be somewhat limited by disk speed. In the extreme example where most of the "render" is actually a "smart render," Vegas performs nothing more than a disk copy. In this case you can get a significant performance increase if your destination disk drive is different than the drive(s) which contain your project media. The destination needs to be a different physical drive, not just a different partition, and ideally should be on a different connection, although most modern disk connections have incredible bandwidth.

For most renders, the CPU is the main bottleneck, and the disk drive is loafing, so it doesn't matter too much.

A lot of my work involves an initial "cuts-only" step which is then smart rendered, so this two disk approach has saved me a lot of time.

I've done over a dozen at a time. I also tend to use a single drive for the source and the output. Each individual render might have taken an hour on it's own. Running them all at once took about half an hour longer than running them one at a time. But, of course, i could leave the computer to go eat, have an evening, sleep, and then see the results in the morning.

Not mentioned yet, but with a multi-core (or multi CPU) system, you can open task mamager, right click on an instance of Vegas, tell it which cores to use, then run another instance of Vegas on another set of cores and edit in that one while the other is rendering. You can then edit and render with almost no slowdown. I do this for many projects, rendering out finished segments of a project to high quality files while editing other parts of the same project.

"you can right click on an instance of Vegas, tell it which cores to use"

how / where is this done?

Oopes, forgot the step where you open task manager. Sorry about that.

all i see is "set priority"

"set affinity" lets you choose the cores. Should have a lot of options in there.

Try "Set Affinity".

Edit: TheHappyFriar beat me.
Willem