Leaving a will is a wise thing to do for many reasons. This can include providing for the future of loved ones, handing heirlooms down to posterity, and wrapping up your affairs for when you pass. Of course, your last will and testament can do so much more than this. It cannot deal with everything though. There are some restrictions on what a will is able to do with your property, finances, and last wishes. It is important to identify what these limits are. Not only can this protect one from unrealistic expectations, but you may also be able to deal with them through other means.
First of all, you may not be able to dictate who gets some of your property. For example, some of your property may be held in joint tenancy. This can be a house that someone jointly owns with a spouse. When one spouse dies, the other, through right of survivorship, will become the full owner of the house, without the hassle of probate. You would not be able to will the house away to someone else. The same goes if the other owner would have right of survivorship through tenancy by entirety or community property. The only way a will could leave that jointly-owned property to someone else if both owners pass away at the same time.
You also cannot hand down property through a will when you have already included it in a living trust. If you have been named the beneficiary of a life insurance policy, you cannot pass this money down through a will either. Anything in a pension plan, IRA, 401k, etc., cannot be willed to someone when you have already listed a beneficiary for these. You may have stocks or bonds that name a beneficiary through a transfer-on-death form. A will cannot change who gets these funds. You would be able to change the beneficiary through the brokerage company. The same goes for anything in a payable-on-death account with your bank. You have to contact the bank itself to change the beneficiary, and you can do so through a quick process.
You should also bear in mind that your will is probably not going to be discovered, much less read, until well after you have been buried and the funeral has taken place. It could take weeks to look at the will. Therefore, you cannot name funeral arrangements in your will. There are other documents that can take care of this, which you can leave with your executor.
Furthermore, a will cannot remove the reality of probate (though a revocable living trust can). You also cannot do anything about estate taxes in your will. Certain types of trusts can, however. Again, a trust, not a will, is the way to go if you want to set up a fund to provide for someone who has special needs.
You also cannot leave property or finances with contingencies attached to them, such as leaving money to a person only if they will marry or divorce someone. You also cannot give money or property to pets. If you want to make provisions to care for your pet when you are gone, you can leave your pet to someone, and then leave that person property to help with your pet's care.
As you can see, a last will and testament may not be able to do everything you want it to. You still have other options to take care of your final wishes, however. With the expertise of a probate lawyer on your side, you can take full advantage of any and every of these.