The Regulation does not only affect who receives your estate when you die. It may also affect:
Who administers your estate. In England, the executors named in your Will (or your closest family members, if you don’t have a Will) collect in your assets, pay your debts and distribute the balance to your beneficiaries. In most EU countries, the beneficiaries themselves do this.  If English law applies under the Regulation, the English system is supposed to apply, but this may cause confusion in countries who are not used to it.
How your estate is taxed. The Regulation does not change the tax law of any country.  However, UK inheritance tax and similar taxes abroad largely depend on who inherits your estate.  If the Regulation changes who receives your estate, this will probably have a knock-on effect on how it is taxed.
Who can make claims against your estate. If foreign forced heirship rules apply, the people who benefit under these rules may claim their reserved shares if your Will attempts to override them.  If English law applies, this may allow claims against your estate by spouses and civil partners (including ex-ones), cohabitees, children and dependants.
Which court decides any disputes about your estate. Each country also has rules about which disputes its courts can decide. If you are habitually resident in a country where the Regulation applies when you die, the default position is that the courts of that country will decide any disputes about your estate. Choosing to apply the law of your nationality can allow the courts of the country concerned to decide a dispute instead, if the Regulation also applies in that country.