Short: it improves by a lot the readability of your text.
Sentences are one of the most important tools in language to organize ideas. A dot is too small and discrete to set apart sentences. Adding a dot ~and~ an uppercase letter right next to it makes a much better separator.
You're welcome to disagree. Since you were generous contributing about spelling - I'm not a native English speaker, btw -, I just wanted to pay back with a suggestion about text structuring and readability.
my thoughts on spelling are that when someone is making an argument, their ability to use a word correctly is a necessary part of conveying their ideas clearly. and spelling a word correctly is a necessary part of using a word, since the spelling evokes the entire history of the word itself: the language and context it came from, the people, time and place that word originated.
i truly am interested in hearing your input on why you think it's important to use casing. change my mind