I think for security purposes, motion sensor lights are much more effective than simply leaving on the light outside.

I think very effective - but take note that you don't create light pollution in your neighbour's yard, this can cause huge problems.

Motion sensor lights do have some deterrence on thieves, but limited.

When installing the motion sensors, try to have them high up so they can't be broken - this definitely makes them more effective.

Burglars always go for the weakest house on the street, so if it has lights go on and off all the time, much less likely to be burgled.

Apart from the light going on and off, there is the expectation that a loud alarm might go off - which is a huge deterrence.

Note also that yellow light is much better than white light for security purposes.

I think that if a burglar wants to get into your home, then a sensor light is not going to do that much.

Yes, but a light going on and off will definitely make any burglar think twice and three times whether the risk is worth it.