I assume it is a PPT? If you save it as a PDF it would be much smaller.
I don't think files size is much an issue these days with all the file sharing resources available--some of which have been mentioned already. I use Box, others use DropBox, OneDrive etc. However, if emailing the document, there is concern for at least two reasons; 1, email servers can reject files for being too large--there are no standards so this varies widely around the world. 2, It's a point of courtesy to the readers because their allocated email space can be used up quickly with large files.