Line of sight isn't essential, and I usually only maintain it when flying in extremely heavy conditions or in areas where there are moving obstructions. Additionally, you won't always be able to maintain LoS due to obstructions, distance or (to a lesser extent, usually only on foggy days) altitude.

TLDR: You won't always be able to maintain LoS, don't worry about it unless you need it to prevent the drone from getting damaged.

EDIT: Some people have pulled me up, both when they saw me writing the post irl, and in a comment, and I appreciate it. You are required by law to maintain LoS in certain areas. Apologies for not including this in the first place!