About the only time I go into one of these shops is when they are insanely busy. At least then you have some chance of browsing around without having to say 'just browsing thanks' multiple times, often to the same salesperson. (What part of 'just browsing' don't they believe!) Every time I have to tell them 'just browsing' heightens my resolve not to buy anything! As for buying anything from DSE or one of the others I'd only do this if the price is incredibly good. However, with their high overheads such as rent to Westfield, their prices are usually not that great.
Reasons for going into one of those stores:
1.) When you want handle an item where 'feel' is important such as a keyboard, mouse, or camera. Then I look online for the best deal or go a retailer that does not push extended warranties etc.
2.) When it is a smaller item at a incredibly good price and one that they can't up-sell me anything on.
It is a long time since I bought any larger item from one of the tri-opoly shops! It's not my fault that they need to sell laptop bags, anti-virus, surge protectors, and extended warranties, and other stuff to make their businesses viable.