Probate is not needed to transfer certain kinds of assets. Specifically, you do not need probate to transfer property that is held in joint names. This is because joint ownership carries with it a right of survivorship of the other owner(s). For example, if a husband and wife own their home jointly and the wife passes away, the husband owns the house by right of survivorship and doesn't need probate to put the title in his name alone. Take note that this rule does not necessarily apply to assets that were jointly owned by the deceased and his or her children.
You also do not need probate to transfer assets that have a named beneficiary. These assets include RRSPs, RRIFs, life insurance policies, pensions and some other assets. When the owner of the asset passes away, you only need to provide a Death Certificate and some information in order to transfer that asset to the person who is named.
Because of these rules, it's quite possible, and in fact is the norm, that a husband and wife can set up their financial affairs using joint property and beneficiary designations so that when one of them dies, the other one does not need to go through probate.
For anyone who is not in that situation, and whose assets are not all going to pass to someone automatically due to joint tenancy or beneficiary designation, the question of whether probate is needed is going to depend at least partly on the type of asset they own.
If you own real estate in your own name alone, or if you own it as a tenant-in-common, your executor will need a Grant of Probate to transfer or sell your property.
If you have assets that will form part of your estate after you die, such as life insurance policies and RRSPs that name your estate as beneficiary, your Executor will need to get probate. This also applies to any assets held in your name alone, such as a bank account, investment, or expensive personal items (e.g. art collection).
If you have a significant amount of money in your estate, your Executor will need probate before he or she can gain access to it.
There are other, less common, reasons why executors must go through probate. For example, the executor might have to finish litigating a lawsuit on behalf of the deceased. There could be a dependent who wants to make a claim against the estate. There could be some question about whether the Will itself is valid or some of its terms might need to be clarified.
It's sometimes hard to tell right at the beginning of an estate whether or not you need to go through the probate process. Sometimes the only way to know for sure is to take the Will to an experienced lawyer, together with information about the deceased person and his or her assets, and ask for an opinion.