Reusing another faculty's material
The culture in different departments is different. I've been in departments where the expectation is that everyone develop their own teaching materials. I've also been in groups and departments where if you asked whether you can use someone else's material, the answer would be "of course".

In general, reusing someone's materials without their consent is poor style. But I would suggest to all young faculty that they ask older colleagues what the culture of the department is. If the answer is "Yes, of course we help each other", then if you want to reuse someone's materials, the right approach is to ask them whether they'd be willing to share their materials.