I do like to place tooltips whenever I feel that the user could benefit from them.
I tend not to place tooltips on controls when I think it's pretty obvious what their effects are.
However, on some instances, I like to place tooltips kind of guiding the user, advising them on non-trivial side effects and giving general tips like:
By clicking on this, a new XPTO will also be created.
Don't forget you can also do XYZ or XPTO.
However, lately I've started thinking that, if I just place tooltips on some controls and not on others, users will be confused because I've started a pattern (i.e. placing tooltips on controls) which I sometimes do not heed.
I also think that, perhaps, users will become used to having tooltips and will miss them if they're not always there.
Is there any consensus on this topic? If I can't put tooltips on all controls, should I avoid placing them on any at all?