17% of people now say that they have left money to charities in their will and that proportion has grown significantly in recent years. I think there was a campaign to encourage people to leave 10% of their estate to charity.
Research also shows that the majority of people consider it when making a will so I think it is something that is growing in popularity.
As for pros and cons. If you leave money in your will to anyone, or any organisation, charitable or not, then there is less money for your main legatees, usually one's children. Apart from that I cannot see any downsides. the upsides is you are helping the charity of your choice.
Also money paid to charities is deducted from your estate before liability for inheritance tax is calculated. If you donate enough money for your estate to fall out of the inheritance tax band, although, from the legatees point of view, it makes no difference to the amount they inherit, you know that the money is going to the causes of your choice, not just being absorbed into general taxation.
If you leave a specified sum to a charity and then the residue to be divided up/left to other named people, then the charity would come first in giving out your assets. I haven't put charities in my will but if I did, I'd give them a percentage share not a specific amount ( if I wanted other to inherit of course)