I normally dont send customers the Vector image or an editable pdf file. That way they cant go somewhere else with it and i lose out on money unless they buy the main file..But i do previews of the finished design etc for them to approve or make changes and even then i only send a somewhat low res that cant be used to re-trace but clear enough to let them see it clear for an ok.. Otherwise save as the largest file and res and it will be just fine. None of my customers ask for a vector etc unless they have other uses for it .
I just picked up a contract for a world wide company and for them i do save the largest and the highest res image for them..So i pick and choose who gets what and what quality.. hope that helps? I use Ai cs6/CC
If you design a logo for a customer, It should be 100% theirs as it's their branding, not your product to keep selling them. You're providing a service.
If i had someone design me a logo for my business, I would like to own the logo and to do what i please to it, as it's mine. Not for the designer to give me half of it and i can only get them to print me what i need.
To the OP:
If you design a logo for a customer, and they're paying to own the file and not the rights to only use it or what ever.
If it's a Raster image, It would be firstly designed in the highest res possible so it's printable on 1220x2440mm signs clearly with headroom.
if it's a vector, PDF highest version.