I always use one and two letter prefixes in VBA. I'm sure I'm the only one that's going to admit that, but I figured somebody needed to be the contrarian.
Of the 18 million lines of VBA code I've written, I've collaborated on about 1,000. If nobody else sees my code, then I'm free to use a convention that I like. If someone else will be working on your code, you should agree on a convention.
I like that it lets me keep my variable names shorter. I could use FileNumber and FileName or I could use lFile and sFile. I don't find one more or less readable than the other. It also helps me use reserved words as variables. If I want to use Replace as a variable name, I can't. But I can use sReplace or lReplace.