Biggest problem is light going on and off like a yoyo due to it being triggered by animals, etc. 

Also light going on and off can be very irritating to neighbours.

Make sure that you don't just rely on your electrician's "wisdom" in terms of what to install, and where to install it.

Generally electricians know just about how to install something something. They know sweet nothing about the right motion sensor for the job, and even less about exactly the right location to install it - so do your research.

Agree, lots of electricians I have had over the years have done a really bad job and even sometimes extremely unsafe jobs.

Make sure  regarding the sensor light you purchase that you understand its beam angle, the range of its motion sensor, and also how bright it is. Very easy to get a stadium strength motion sensor flood light to light a tiny garden, if you are not careful!