That depends on what you're trying to protect against.

If you're worried about security problems, then using placeholders will be enough.

If you're worried about data constraints, then you still need to check your parameters. If the database allows a value that you don't want in it, you'll have to validate the user input to ensure that. If the user tries to pass in a value that the database does not allow (a string rather than a number, for example), then the database will throw out an error when you try to put that in. Either way, some kind of validation before the data reaches the database could save you one headache or another.