Variable expenses are those expenses that track directly with sales. If sales stop they stop. These are expenses like supplies used to support in the making of your product or doing your service. Such things as shipping cost for raw materials for your product or service. If you have no sales then you're not going to be purchasing materials so your shipping cost for those materials will stop as well. As an example, if you have a lawn mowing business and there are no lawns to mow, then you wouldn't be buying gasoline to travel to your lawn mowing site. These kinds of things are variable expenses. If you're producing a product, it would include supplies used to produce that product like sand paper, glue, finishing materials, cutting tools, etc.
Once you have a plan in place, it's important that you follow it. If you're achieving your goals you should stick with the plan. If you are not achieving your goals then you will have go back, analyze your plan to find out what is working, what is not working and why it is not working. A plan is not etched in stone. It is subject to change. As time goes on, things change in this world and businesses like everyone else are subject to change. A good plan will reflect changes that a company has to make to keep it competitive and successful.