Question

line wrench
a line wrench is a special type of wrench designed especially for loosening pipe and cable fittings. resembling a combination between a box - end and open - end wrench. this wrench design grips the nut on more edges, so you can apply more force to either loosen or tighten.
line wrenches are commonly used to loosen/tighten brake, power steering, transmission/engine oil cooler line fittings and cable ends. an open end wrench should not be used to initially loosen these types of connections, because the risk of slipping and damaging the fitting is considerable.
why is there a small opening at the end of a line wrench?
this enables the wrench to be positioned around the fitting of a pipe or cable.
this enables the tool to be used more quickly.
this prevents the maximum transferable force from becoming excessive.

Explanation:

The small opening at the end of a line wrench allows it to be placed around pipe or cable fittings. It also enables quicker use as it can be more easily positioned. And it does not prevent maximum transferable force from being excessive as its main function is related to positioning and usability around fittings.

Answer:

This enables the wrench to be positioned around the fitting of a pipe or cable., This enables the tool to be used more quickly.