When you encounter some logical markup, i.e. some things that belong to the same “class” and should be displayed equally (like names etc.), don’t use \textit and the like to format them but instead define a new macro to format those things. Then you’ll be consistent and you can change things later on quite easy.

Example
In your text there are lots of names, that should be – at the moment – displayed in italics. Then define a macro \person (or what ever you consider a meaningful name for these things) to format the output:

This gives you the opportunity to change the styling later and even do some fancy stuff like highlighting only the first occurrence of a name or generating an index with those names etc.

Some will say: “But I can just search and replace \textit later.” Yes but not if you used it also to format book titles or other things that should keep the italic format ;-)

Today I took over a client’s project containing lots of definitions like

etc. Don’t do this! It’s absolutely awful to maintain and in some month when you get back on your document you’ll probably have forgotten what all those shortcuts mean. On a first sight they save some time while typing but that is actually a task for autocompletion and a proper editor. Furthermore things probably get complicated if you redefine (\renewcommand) macros that are already defined without knowing what you do and which other packages rely on the original definition …

It gets even worse if you share your documents with someone else and force them to learn you abbreviations, while e.g. \beta is perfectly clear for everyone. Not to think about a case where two authors use different definitions/abbreviations like

Thus: Don’t use shortcuts instead of the original macros and use “speaking” (meaningful) names for your macros.

Post updated according to Clemens’ and Moss’ comments.