We will use 左面or左边 more in spoken language, but 左侧 in written language.

Hi, That's a great question! To my understanding, "左侧" is usually used to point out stuffs alongside the road. For example, McDonald is located on the left side of the street（麦当劳在这条街的左侧，we don't say 麦当劳在这条街的左面） .“左面” is used to point out the location of something compared with an object, including people. For example, the mountain is located on your left side（这座山在你的左面）。This building is located on the left side of that building. （这栋楼在那栋楼的左面）

不严谨的来回答，在中文的日常使用过程中，大部分情况下，左侧 and 左面 ，都是是一个意思。 比如：在我的左侧有个东西 and 在我的左面有个东西，这两句话是一个意思。 比如：房子的左侧有只狗 and 房子的左面有只狗，这两句话是一个意思。 某某物体的（左侧 and 左面 and 左边 and 左方向）有个东西，基本算是一个意思，中国人都是混合使用。