Currently running Win 7 as a guest OS on Macbook Pro (Mac OS 10.7.5). I have a 750GB disk which is currently allocated 80GB to Host and 670GB (pre-allocated) to VM. (Recognizing now, this was a rookie mistake.) Unfortunately the VM is constantly getting shutdown due to running out of space on the HOST. The host is regularly using 70-73GB of the 80GB. The VM, on the other hand has about 300GB of free space. I've seen lots of posts about how much space to allocate to the Virtual Machine (guest), but haven't found any posts on recommendation for the host system.
Here are my questions:
1) for the life of me I can not understand what is taking up 70GB+ of space on the host. I installed Disk Inventory X and the top 4 folders using disk space (other than the VM) collectively add up to about 20GB. The rest of the folders are <1MB. Where is the rest of my disk space? How can I "recover" it? If I can find the answer to this, I could potentially avoid rebuilding the VM.... 
2) If I were to rebuild my VM (because, apparently, I can not reduce the VM and give back the recovered space to the host and can't find the missing ~50GB in step 1 above), how much should I allocate to the host to ensure I don't run afoul of the Host running out of space? I ask the question this way because I anticipate growing needs for the VM and want to allocate as much as I can to the VM without choking the Host.
Any/all help appreciated.
Thanks!
After reading your post I can't help but think, for a moment anyway, under the circumstances why on earth don't you just have a PC to run Windows. (Although Windows does run better on a Mac then a PC! 
) I know you said "(Recognizing now, this was a rookie mistake.) " nonetheless to me pre-allocating ~90% of the Host's HDD/SSD, regardless of its size, for a Virtual Machine (or just about anything else) is absurd and would never do it under any circumstance.
Anyway, I think that regardless of what's taking up space other then the Virtual Machine is irrelevant and the Virtual Machine's virtual hard disk should be resized downwards however this cannot be done once a virtual hard disk is partitioned/formatted however there are options. Because you do not have adequate free disk space on the Host to perform any maintenance on the Virtual Machine you'll need to use external storage like a Firewire/Thunderbolt/USB HDD to help get out of this mess.
Two choices come to mind, either use disk imaging software like Symantec Norton Ghost to do disk to disk imaging to a smaller right-sized disk and then swap out the virtual had disks or install VMware vCenter Converter into the Virtual Machine and then create a new VM from within the VM to the external storage while customizing the size of the virtual hard disk to a smaller right-sized disk as you walk through the Wizard. Personally I'd choose to use disk imaging software.