I'm afraid to admit it, but there are still many companies and businesses that use their logo, only as a JPG image.
And why is it wrong to have it in JPG (or JPEG)?
It's not precisely wrong, the wrong thing is not having more options like in vector formats.
First. It may be obvious, or not, but a JPG (or TIF, PNG, GIF, PSD, etc.) is made of pixels and by a limited number of them. Once the logo is created in that format, you can make it smaller and it won't be a problem.
But if you want to enlarge it, that image will be deteriorated because more pixels are needed, which does not exist and have to be invented.
What you get is a logo with jagged or fuzzy edges. In addition, a JPG is a compressed format, that means that the quality of the image is even more affected.
This looks bad, the logo looks bad and It could lead people to think that the company is careless and not reliable.
I'm not against having the logo in pixels format. What I am against is that this is the only format available.
What is correct?
Definitely the best thing is to have your logo in more than one format, which can be in pixels (personally recommend PNG rather than JPG) and a file in vector format that can be EPS, AI, SVG or even PDF (Beware of the latter because It can be a bitmap also, depending on how is created).
Why is this important?
First, because of the quality of your image. And second, because as your company grows it has more needs. Sooner or later you will need it.
It may sound very technical. But any respected designer or printer will know what to recommend you and help you to understand it.
Some time ago I discovered nojpeg.org. They reaffirm why you should not have your logo only in JPG.
If this is your case and you don't have your logo in vectors, contact me, I can help you.
Funny fact: Perhaps there is something worse than a JPG logo, and it is a JPG logo inside a Word document. Please don't do it, as designers, we hate it.