We often hear that reducing energy use is good for the environment, and it most certainly is. What we don't often hear, maybe because it's too complicated, is how the energy portfolio of your area affects your environmental impact and what your energy efficiency upgrades will mean. An energy portfolio is basically the breakdown of what sources an area, a state for example, uses to generate electricity. Different energy sources have different environmental impacts; coal creates a lot of air pollution, nuclear creates hazardous waste, but very little air pollution, Using less electricity in an area that generates a lot of wind energy will mean something very different than using less electricity in area that uses electricity generated from coal, which is why you should think about your energy efficiency upgrades strategically if you're concerned about your environmental impact.
As energy sources vary depending upon location, we'll only be able to talk about hypothetical situations here to illustrate different ways that energy efficiency upgrades relate to energy portfolios. Let's start by discussing a home in an area that uses entirely coal energy that is heated with natural gas. In this home, doing upgrades that either increase heating efficiency or reduce electricity usage will both reduce climate change-causing greenhouse gas emissions, as both electricity and heat are derived from fossil fuels. In this situation, doing any upgrades that reduce energy use, whether that energy is for heating or electricity will reduce your environmental impact and contribution to climate change. However, if instead of coal your energy was produced at a nuclear plant, reducing your electricity consumption would have a less direct impact on you contribution to climate change, though it would reduce your environmental impact, because nuclear energy does not create significant CO2 emissions after the fuel is mined and transported. In this situation you would do well to focus on heating efficiency upgrades before looking at your electricity use.
There's no way to produce electricity at the scale we use it without having some environmental impact-- even solar and wind hurt the environment through changing land use and the impacts of mining the materials they are made of and transporting the panels or turbines. However, what we call renewable energy sources have a much lower environmental impact than non-renewables, even if that impact isn't zero. If you are using energy efficiency measures as a way to reduce your environmental impact, you should not only consider where the most efficiency gains can be made but the impact of reducing your use of electricity versus heating fuels. Sometimes choosing smaller efficiency gains can actually result in a greater reduction in your environmental impact.