Why do some LEGO City vehicles have tiles in their chassis? While building 60150 Pizza Van, I noticed that the first few steps of building the eponymous vehicle have you place lime green 1x2 tiles in specific positions and black 1x2 plates in others:



These then get covered completely by light grey 2x16 plates (although you can still see them just behind the wheels and mudguards of the finished model):



A similar use of tiles appears in other LEGO City vehicles, such as the ambulance in 60204 LEGO City Hospital.

Why are tiles used in parts of the chassis construction? Is it to (slightly) reduce the number of studs holding onto the tubes of the 2x16 plates, thereby making them easier to remove when taking things apart later?
I asked one of the set designers at LEGO, Samuel Johnson, on Twitter. Here is our conversation:

This to aid in the building flow for children aged 5 and up. Easy to spot on the page, easy to find in the pile of bricks :)
— https://twitter.com/Spider_Sam_LEGO/status/1037914372897681409



Ah! Do both the colour and the shape (studless vs studded) contribute to this?
— https://twitter.com/NOVALISTIC/status/1037914613847740416



Depends on the model :)
5year olds aren’t very strong, so it can make it easier to build
— https://twitter.com/Spider_Sam_LEGO/status/1037967767847227392



That makes sense. Too many stud-and-tube connections can make building difficult even for me at times. Thanks for answering!
— https://twitter.com/NOVALISTIC/status/1037994518295994368

So, it's an interaction of several factors including ease of following the instructions, as well as ease of physically attaching elements together (and, presumably in turn, disassembling them).