That is when the software write down the data to you hard drive .
Regular HHD are very slow as lots of data is written down . You see everything you do using the software is saved down to your HDD in real time before you even export it , so everything is saved to your project folder of your scanning session
I did scanned full body scans all at once and it took very long to process and I am using M2 SSD and 64GB of RAM , and the fact that you can do that even with 16GB of RAM the processing of fusing and meshing will take a while . And you will need to fuse the mesh between so not sure if you can do that all at once .
Regular SSD are not the fastest any more on the market but it should make your work much faster already .
Regarding how much points is ok, it all depends of the model surface, is it smooth, is it raw , a lot of features etc…
Usually I decimate my models to around 250K it holds well the details but I do that in Revo Studio .
If you have an object that do not have too much of fine details change the meshing to 5 / 5.5 it will already speed up the process , if you did not liked the result , you can still import the already saved fuse files from your project to Revo Studio and mesh it there , you will have undo so you can adjust the level according to your needs.
Also try using the AUTO settings if you are not sure how much points is needed for your object .
Setting everything on the highest settings don’t means you get the best quality results . Sometimes it make things looks worse .
And most important focus on the captured cloud point before fusing , see if there are any artifacts , it is smooth, has holes or not , evaluation of the point cloud before fusing will result in faster processing time and better mesh .
Don’t use more than 360 frames at max per full rotation while scanning to avoid overlapping point that will slow down all the process . Usually 20-30% of scanned data is removed while fussing and meshing . As it is not usable so the first step is most important .
Now imagine MINI 3D scanner that capture usually 36 millions of points with a very small objects … the process takes long even on my workstation .
Learning curve is big if you are new to 3D
After 24 years I still learn new stuff on a daily basis. It is never ending process .
But without knowing what you are dealing with , it going to be little harder to understand the whole process .
However nothing is impossible, as I see people doing great scans even if they can’t edit a simple 3D model .