You have to be careful when removing fields from a module. Some fields are simply created to store value and removing it has no adverse effects. But a field can be hardcoded in the module - via some callbacks, pre or post processing methods, referenced in some custom javascript, etc.
Before you remove a field you need to inspect the code to make sure that it will not break the module. Especially in Inventory module which is quite complex I would be extremely careful with removing fields. Hiding a field (making inactive) is generally safer approach.
If you don't want to use a field but for some reason it is hardcoded and can not be deleted - create another page (split) and move it to that page making room for other fields on the main page of the record.
