The only reason I can think of why using just one school could be a bonus is that you will then be using the same techniques, checks, etc, right throughout the whole course. Or at least you will do if your school has standardised everything.
But on the other hand, that might be considered a disadvantage. Far better to use a variety of schools, and learn a variety of different ways of doing things. That way you're better equipped to choose a method which works best, and you're also more likely to have come across the techniques which are used in other environments if you subsequently fly from somewhere else.
If the schools are spread out geographically (e.g. different countries), you will also get experience of a variety of different flying environments. So maybe use a UK school for your PPL and IR, a Canadian school for your hour-building, an American school for your CPL, etc.....
If you are offered discounts, watch out. First of all, do they want payment up front? Never pay more money up front than you would be able to deal with loosing. Secondly, check whether you can save more money by shopping around.
FFF
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