Yes they can be a pain especially on a hot day, yes we all want to earn money but I
want it to be as handy as possible and outside work is a lot handier than insides.
Cons....
You risk dirtying the customers décor or breaking ornaments even if they are not sitting on the sills.
Being accused of stealing if something gets misplaced in the property.
There will nearly always be something in front of a window like a bed or dresser which will be a pain to move.
Blinds, some of these can be a nightmare I had some in a property a while back where they just wouldn't stay up.
Annoying kids who follow you around touching the glass you have just cleaned.
And worst of all cleaning the glass of a property where the person smokes.
Pros..
If you have an important customer its a good way of keeping them happy, that's the one and only reason
why I clean interiors.