Think of it like fuel economy. A car with better fuel economy will go further on the same tank of petrol. The petrol is being used more efficiently and less is needed for the operation of the car. An old car with poor economy, will be guzzling petrol. To move away from that analogy, insulin resistant people will often not be able to maintain a balance and still run smoothly if uneconomically in the long run. Their ability to maintain a normal blood sugar may be compromised, and this may lead to type 2 diabetes.
So if you are more insulin sensitive, you will need less insulin (either provided by your pancreas or, by an injection or pump) to do a certain task or deal with a certain amount of food, than if you were less insulin sensitive/more insulin resistant.
Most people with Type 2 will be considered insulin resistant, through such mechanisms as visceral weight. There is nothing stopping T1s from having similar issues, or other similar ones such as possible neutralising reactions by the body to foreign insulin. Insulin resistance is generally the opposite of insulin sensitivity.